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New Technique For Making JPEG Images Copy-Evident

CmdrTaco posted more than 3 years ago | from the believe-it-when-you-see-it dept.

Graphics 139

Gunkerty Jeb writes "The days of wondering whether those drunken sex party photos are indeed the Olsen Twins, or if they are just the Mary-Kate and Ashley's faces photo-shopped on the bodies of Lindsay Lohan and Amy Winehouse are OVER! A group of academic researchers at the University of Cambridge has developed a new technique for making JPEG images copy-evident, so that users can tell whether an image has been recompressed and copied."

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139 comments

PrtSc (0)

badran (973386) | more than 3 years ago | (#35127656)

Print Screen.

Re:PrtSc (5, Informative)

gid (5195) | more than 3 years ago | (#35127740)

Nice try at getting fast karma from a first post, but that's not going to work. The screen shot will already be of the compressed image, and will still show signs of re-compressing it.

Re:PrtSc (3)

ElectricTurtle (1171201) | more than 3 years ago | (#35127798)

See, now I can tell it's a Photoshop from some of the pixels and having seen quite a few Photoshops in my time.

Re:PrtSc (0)

Anonymous Coward | more than 3 years ago | (#35128240)

Or you could apply logic, as in "Hmm. Neither one of Mary-Kate or Ashley are D-cups with their clothes on, I'll bet this picture isn't real".

Re:PrtSc (1)

bytethese (1372715) | more than 3 years ago | (#35128016)

I see your point if it was compressed again using JPEG, but what if GIF or BMP, etc was used. Would that make a difference since they would compress the image using a different algorithm?

Re:PrtSc (1)

phantomfive (622387) | more than 3 years ago | (#35128168)

GIF or BMP would be fine, since they are lossless. Whatever you get on the screen will end up exactly reproduced next time. The drawback is the compression ratio isn't nearly as good, so people tend to use JPEG for photorealistic images, which is why this technique is promoted to work with JPEGs.

Interesting technique, but clearly needs some work (since it only works on certain regions of some images).

Re:PrtSc (1)

TheThiefMaster (992038) | more than 3 years ago | (#35128770)

Gif may be technically lossless, but only if you only want 256-colours. These days "lossless" means on 24-bit colour.

Re:PrtSc (0)

Anonymous Coward | more than 3 years ago | (#35128854)

GIF lossless???!?? Isn't the whole point of the format that it knocks back the color pallet to ~256 colors? I suppose its lossless if the image you started with was only 256 or less colors but photos usually start to look pretty bad if they have any less than a few thousand colors. BMP is lossless I suppose, as long as you don't choose a lower BIT file types (24-bit, 256 color, 16 color) from your original when re-saving.

Re:PrtSc (2)

_0xd0ad (1974778) | more than 3 years ago | (#35129484)

Well, one of those palette entries can be transparent, so if you just stack enough GIF images on top of each other...

Okay... I keed...

Sort of...

Re:PrtSc (1)

gid (5195) | more than 3 years ago | (#35128920)

Well saving it in a lossless format is always going to be a way around any re-compressing artifacts. No "Print Screen" needed. Just load up the jpg in photoshop, do editing and then save as png.

Image sites that wish to deter fake images could force jpeg encoding, or make a jpeg available, maybe going as far as using something like tineye.com does to help find the original and flag the picture if they differ too much.

Re:PrtSc (1)

jbengt (874751) | more than 3 years ago | (#35129056)

jpeg also comes in lossless flavors

Re:PrtSc (0)

MobileTatsu-NJG (946591) | more than 3 years ago | (#35128202)

I'm sorry man, I accidentally modded your post as troll when trying to mod it as insightful. I'm posting here to remove that moderation.

You're absolutely correct. When you take a screengrab of a JPEG and save it as a JPEG again, you're re-compressing it. It's a bit like playing a 128kbit MP3 from your iPod, hooking it up to your computer via the audio cable, recording it, then compressing it again at 128k. You're going to have accumulated information loss.

Badran and a couple of twits with mod points must be confused and think this is a story about preventing people from downloading JPGs.

Re:PrtSc (1)

sexconker (1179573) | more than 3 years ago | (#35129320)

Nice try at getting fast karma from a first post, but that's not going to work. The screen shot will already be of the compressed image, and will still show signs of re-compressing it.

Nice try at getting fast karma from a first post correction, but I'm still going to correct you.

Anyone copying an image will have no problems. Copy-evident my ass, the file is 100% the same if I grab it and throw it in a torrent.

As for editing to remove watermarks / logos, the recompression will only show the message if your quality is below a certain threshold.
If you edit an image to remove the owner's information, and you see a "THIS IMAGE COPIED FROM SITE.COM" message, just save it at a higher quality.

Inserting the message will be a balance between visibility on the original (you want this low) and sensitivity to recompression (you want this high).

And if someone is insistent on using a low quality jpeg after editing an image you own, they can still easily defeat the scheme by doing an extremely slight blur on the entire image.

So the bottom line is that no, this isn't a copy-evident feature, it's an edit-evident feature, and one that is trivial to circumvent.

Re:PrtSc (0)

TheThiefMaster (992038) | more than 3 years ago | (#35127822)

This is a stenography-like technique, print-screen will get you the uncompressed image but as soon as you compress it as a jpeg it will show the message again.

Of course this would be voided by using lossless compression or just using the original image.

A variation could even work on a resampled resize of the image, in which case it doesn't matter how you save it, it's "use the original or else".

Re:PrtSc (0)

Anonymous Coward | more than 3 years ago | (#35127904)

Stenography?

You kids are hilarious.

Re:PrtSc (4, Funny)

$RANDOMLUSER (804576) | more than 3 years ago | (#35128146)

(keys desk intercom) Miss Jones, come in here! And bring your steganography pad!

Re:PrtSc (2)

mlts (1038732) | more than 3 years ago | (#35128644)

I want my secretary to use a one-time pad for transcriptions.

Re:PrtSc (1)

Smidge207 (1278042) | more than 3 years ago | (#35127852)

How about I take a hi-res picture of the screen with a digital camera?

Re:PrtSc (0)

Anonymous Coward | more than 3 years ago | (#35128066)

True. I did a proof-of-concept here:
http://folk.ntnu.no/asmunder/spoofed.png
where the upper part is the print screen, and the lower part is recompressed with jpeg at quality 60. As you can see, the technique has failed.

Re:PrtSc (1)

fastest fascist (1086001) | more than 3 years ago | (#35128224)

As even the summary mentions, the technique applies to jpeg-compressed images.

Re:PrtSc (1)

sexconker (1179573) | more than 3 years ago | (#35129346)

As even the summary mentions, the technique applies to jpeg-compressed images.

As even the post you replied to mentions, he grabbed a messaged-jpeg via print screen, and recompressed it via jpeg at "60" quality (I'm assuming that's photoshop's "60").

The screenshot provided is in two halves: The top half is the original uncompressed image, and the bottom half is the recomrpessed image. The file format png was chosen for the combined view specifically to avoid compressing the top half and compressing the bottom half a second time.

good luck with that (-1)

Anonymous Coward | more than 3 years ago | (#35127682)

but there were too many witnesses to claim that the photos of cmdrtaco getting fucked by a horse were fake.

I'm not a computer genius (0)

abbynormal brain (1637419) | more than 3 years ago | (#35127692)

but to someone who is, PLEASE PLEASE PLEASE insert a "Rick Roll" into a JPEG. RE: "relies on a complex method for inserting a large message into an image, which will only become visible once the image is copied and recompressed at a different level of quality"

Image protected, but is it useful? (4, Interesting)

Rashkae (59673) | more than 3 years ago | (#35127726)

If the image can't be re-encoded or re-scaled without the watermark becoming visible, then it probably can't be resized for viewing either. So the only images can can really make use of this 'tech' are the ones that are already shrunk to their smallest desirable viewing size. I'm not sure how much use this will really have.

Re:Image protected, but is it useful? (2)

Hatta (162192) | more than 3 years ago | (#35127932)

The only images you're going to want to protect are the ones you've distributed on the web.* Those are going to be the ones that are already scaled down. You do scale down your images before you host them, right?

*if you've decided to be a dick about copying, you're probably not going to be distributing your high res source image

Re:Image protected, but is it useful? (1)

amicusNYCL (1538833) | more than 3 years ago | (#35128204)

You do scale down your images before you host them, right?

Of course. Everyone posting their copyrighted images to Flickr, Tumblr, and other sites missing vowels always resize their images first, including making their own thumbnails. No one relies on the site to make its own thumbnails or show the image at various sizes.

Re:Image protected, but is it useful? (1)

Hatta (162192) | more than 3 years ago | (#35128632)

If you're using a remote app to resize your files, then the remote app can apply this filter at the same time. No big deal. The point is that there's no reason for the end user to have the source file, especially if you're only delivering a low res copy of it.

Re:Image protected, but is it useful? (1)

Strange Ranger (454494) | more than 3 years ago | (#35129302)

If somebody is copying it for a "friendly" reason, why not use a link? If they can't embed a link, then they can have a watermark. Still not good enough? Well how about asking? That's not being a dick. That's preventing others from being dicks.

Re:Image protected, but is it useful? (1)

cdpage (1172729) | more than 3 years ago | (#35128134)

If you take a photo of Prince William with some other woman kissing. You would send not a low res image to a newspaper you would send a small cropped edited one with this invisible water mark. If the Paper wants to use it they would need to ask you for the image in the given size. If they try to edit that they see the water mark and can't print/put to the web.

When they do post this image to the web with out altering it, and you see that Huffington post has this photo, you copy image to your desktop, open it in photoshop, and stick your face on his head. Save As...

And there it is. Oh, this image is Copyrighted. Well what ever, i just want to send to my friends anyway... Maybe a PNG, TIFF... Screen grab at 100% there. there we go.

its a deterrent, as much as it is a notification. This is Copy righted. distributing this image for profit as your own may be illegal... blah blah blah.

This Tech may be useful for stock photography sites too. rather then have a water mark all over the image, a hidden one might be nice for conceptualizing.

Re:Scaling should not be affected (4, Informative)

b4dc0d3r (1268512) | more than 3 years ago | (#35128514)

If you read the article, they are depending on the JPEG compression artifacts for the watermark display. Resizing should not cause this because you are deling with the uncompressed image data.

Resizing and then saving as a JPEG will result in re-compression and the watermark appearing. Saving as anything else bypasses this completely.

This is only useful when you know what conditions will be applied. The example they give near the end, uploading to youtube, will apply only as long as youtube does not change their settings. Then you have to change your thresholds and all of your protected videos in the wold are unprotected.

Re:Scaling should not be affected (1)

cforciea (1926392) | more than 3 years ago | (#35129348)

Actually, after playing with it a little bit, it becomes readily apparent that resizing (at least in Opera) affects this the exact same way that re-compressing the data as a jpeg does. As I run through the compression qualities in paint.net, I see the exact same patterns of compression artifacts in the images that I do when scrolling through zoom levels in my browser. Really, image scaling and compression are very similar problems, so this shouldn't surprise anyone.

This means two things. First, this technique currently only works at very specific jpeg compression levels (and on this particular image, it only works at qualities way lower than what I'd ever use for even a 10 minute cheesy photoshop hack job, which means it is probably just the default for MS Paint), so circumventing the protection is even easier than switching formats (just slide the quality bar over to the right when saving in any real image editing software). Second, and more importantly, even if they could make this technique universal, it would have the exact problem with resizing that GP mentioned.

Re:Scaling should not be affected (0)

Anonymous Coward | more than 3 years ago | (#35129656)

"If you read the article..."

You must be new here. ;)

Re:Image protected, but is it useful? (2)

Danh (79528) | more than 3 years ago | (#35128736)

The original image can be resized without showing the watermark, see their demo page [cam.ac.uk] (and press Ctrl +/- if you browse with Firefox). But so can the re-encoded picture, it shows the watermark only at the zoom level of 100%.

From this I suppose that there is also one zoom level at which the original picture shows the VOID watermark (you better choose it to be an odd value)!

Re:Image protected, but is it useful? (2)

mobby_6kl (668092) | more than 3 years ago | (#35128764)

I'm not sure what the method in TFA does since I didn't read it, but this isn't cold fusion.

Watermarking has been available for a while, even as a standard Photoshop filter. Just for a test, I applied the Digimarc watermark to a 18MP shot of my dog, and then resized it to 40% of the original size. The result? The watermark could be still read, albeit with a lower indicated watermark strength. Likewise, resaving it multiple times as a JPEG just slightly decreases the strength. If you aren't an idiot and don't start win a huge DSLR photo, it should be fine down to the common web sizes.

Of course if somebody knows about it and deliberately tries to destroy the watermark, I'm sure it won't be a huge problem. Like by applying a healthy dose of Gaussian blur.

not really new (1)

v1 (525388) | more than 3 years ago | (#35127728)

identification of transcodes is very well-worn technology among MP3 users. Where people will take a 128kbps and transcode it to 320 and cause a small riot when people get upset getting a 320 that sounds like crap.

I imagine this is not really any different. Just look for the telltale squared loss and clipping, but in the image spectrum instead of the audio spectrum.

Re:not really new (2)

0100010001010011 (652467) | more than 3 years ago | (#35128116)

Error Level Analysis [errorlevelanalysis.com] has been up for quite some time. It's not a hard set "this was a 'shop", but it's pretty good.

Re:not really new (1)

v1 (525388) | more than 3 years ago | (#35128866)

>>by 0100010001010011

Nintendo fan?

Not ready for commercialization (4, Informative)

ColoradoAuthor (682295) | more than 3 years ago | (#35127730)

From the original paper [cam.ac.uk] : "The technique now needs to be extended to handle arbitrary photographs, not just uniform regions."

Good enough for me (1)

mangu (126918) | more than 3 years ago | (#35128172)

"The technique now needs to be extended to handle arbitrary photographs, not just uniform regions."

Great, I've always wanted some way to tell if the blank wall in the background had been edited and replaced by another blank wall...

Re:Good enough for me (1)

cforciea (1926392) | more than 3 years ago | (#35129374)

Actually, that's exactly what you couldn't detect. The VOID only would appear in uniform areas, which means that in addition to all other stated problems with this technique, you can still photoshop Ryan Reynold's head onto a porn star's body as long as you use a magic wand tool and/or a paint bucket on any uniform areas of the image.

Slightly Misleading (2, Insightful)

sltd (1182933) | more than 3 years ago | (#35127754)

If you're really serious about putting Mary Kate and Ashley's head on Lindsay Lohan and Amy Winehouse's bodies, like it says in TFS, you'd use RAW. Then, you can compress everything together. Besides, if you upload that to photo sharing websites (especially Facebook) there's a high chance your picture would be recompressed, so it would have the compression artifacts whether it's been altered or not.

Fail.

Re:Slightly Misleading (5, Insightful)

jeffmeden (135043) | more than 3 years ago | (#35127874)

If you're really serious about putting Mary Kate and Ashley's head on Lindsay Lohan and Amy Winehouse's bodies, like it says in TFS, you'd use RAW. Then, you can compress everything together. Besides, if you upload that to photo sharing websites (especially Facebook) there's a high chance your picture would be recompressed, so it would have the compression artifacts whether it's been altered or not.

Fail.

Have access to RAW files of the aforementioned act involving Lindsay and Amy, along with ideally angled shots of the Olsen's faces? Didn't think so. So, you go to google images and start digging. What you find (in the ideal world this paper is picturing (ugh no pun intended)) is that every content creator (from the pr0n guys to the papparazzi that took the olsen's picture) have applied this filter to their work, and as such your efforts are for not. Don't get me wrong, there are tons of problems with this whole idea, but saying "well raw doesnt have artifacts anyway" is a bit of a fail.

Re:Slightly Misleading (0)

Anonymous Coward | more than 3 years ago | (#35128394)

your efforts are for naught

Re:Slightly Misleading (0)

Anonymous Coward | more than 3 years ago | (#35129060)

and as such your efforts are for not.

Actually, their efforts are for naught.

Re:Slightly Misleading (1)

taustin (171655) | more than 3 years ago | (#35129188)

Very true. Changing the format to, say, BMP, before doing the shopping, however, has a certain potential. Plus, TFA says this only applies if you change the compression level. So don't change the compression level. (Plus, I suspect it will be about ten minutes before somebody comes up with a Photoshop script that will strip this out, assuming existing watermark removing scripts won't already.)

Re:Slightly Misleading (0)

Anonymous Coward | more than 3 years ago | (#35129654)

>>and as such your efforts are for not

Grammar Fail.

Not 'not', NAUGHT, dude.

Re:Slightly Misleading (1)

Anonymous Coward | more than 3 years ago | (#35128052)

Yes, the only thing this is useful for, is misleading a Judge into thinking that a digital picture may not be altered. It's past when pictures were able to be used as evidence. It's now really hard to rely on images, but many people would still believe in them.

I brief computer graphics class can show you how easy is to fake pictures. It doesn't matter if you have a "certificate" or some authority to mark the pictures, because that could probably be faked too.

Re:Slightly Misleading (1)

A Friendly Troll (1017492) | more than 3 years ago | (#35128364)

If you're really serious about putting Mary Kate and Ashley's head on Lindsay Lohan and Amy Winehouse's bodies, like it says in TFS, you'd use RAW.

No, you would not, unless you took all of those photos yourself. You will not find any RAW downloads of those anywhere on the web.

Re:Slightly Misleading (3, Insightful)

MobileTatsu-NJG (946591) | more than 3 years ago | (#35128382)

If you're really serious about putting Mary Kate and Ashley's head on Lindsay Lohan and Amy Winehouse's bodies, like it says in TFS, you'd use RAW.

Uh, yeah, by 'use RAW' you mean: "take photos of these celebrities yourself".

...so it would have the compression artifacts whether it's been altered or not.

Unless you took the RAW photos yourself, there would still be different artifacts from each of the pictures you used to do the composite. More artifacts won't change that. Besides that, Facebook resizes the image THEN saves it, again altering the new artifacts in a not-so-subtle way.

You haven't shot this down at all and it's obvious that people with mod points don't understand this topic.

Re:Slightly Misleading (0)

Anonymous Coward | more than 3 years ago | (#35129208)

Even if they can protect the images with a watermark that survives recompression, it doesn't matter. I can still FAP over a watermark.

social problem, technical solution (1, Insightful)

FuckingNickName (1362625) | more than 3 years ago | (#35127776)

Sigh, another pointless arms race brought on by businessman-academics selling snake-oil.

I wonder how long it will take to overcome the "message appears when a particular specific combination of recompression settings is chosen" anti-fraud-or-something technique. I mean, it's such a novel idea and there are so few alternative combinations of recompression settings.

Re:social problem, technical solution (2)

madbavarian (1316065) | more than 3 years ago | (#35128006)

How long before browsers automatically low-pass filter these broken jpegs? If not, then the browser is going to have a hard time resizing the jpeg if this high frequency noise is so large in amplitude that it causes clipping in the jpeg calculations.

Re:social problem, technical solution (2)

Half-pint HAL (718102) | more than 3 years ago | (#35128064)

Consider this: with several different HD sizes in frequent use, and even more computer screen geometries, for any given video you're going to find a lot of legitimate users viewing a radically resized version, so indiscriminate interference is unworkable. So who is this "specific combination" aimed at? YouTube. Could YouTube change their settings to get round this? Yes. Would YouTube change their settings to get round this? No. Because they would then be actively facilitating piracy and in breach of the DMCA. Any change of the YouTube reencoding settings would have to be thoroughly justified with some other goal, or they'd see themselves sued to bits.

HAL.

Re:social problem, technical solution (1)

betterunixthanunix (980855) | more than 3 years ago | (#35128476)

I wonder how long it will take to overcome the "message appears when a particular specific combination of recompression settings is chosen" anti-fraud-or-something technique.

This is basically what happened when the RIAA tried to impose audio watermarking on CDs; the idea was that if a watermark was destroyed by MP3 compression, the CD player would refuse to play the track. Clearly, this was a stupid idea, since people just played the MP3 file from their computer (did anyone actually think people would spend their time and money burning MP3 files to CD?), and it did not take long before people had Internet connections that could be used to quickly download less compressed (higher quality) MP3 files -- defeating the system once and for all (in fact, the system had been defeated before it was deployed, but let's just assume that the researchers had not been able to simply remove the watermark). Now we have a dozen different ways to encode audio which will not destroy the watermark, but for some reason CDs are still being shipped with it.

Trivially defeated watermark (0)

Zerth (26112) | more than 3 years ago | (#35127784)

Mung bits, continue with faux slash fanfic.

Defeated by a light smoothing of the image? (1)

jandrese (485) | more than 3 years ago | (#35127786)

The technique described in the article sounds like it would be defeated by applying a filter to the image before re-compressing it. It sounds like it is very dependent on having the encoder stumble over very specific bits in the image, and messing with those bits is likely to mess up the effect. Worse, if someone goes and finds your message (by encoding the image several times), it seems like it should be pretty easy to reverse the effect.

Re:Defeated by a light smoothing of the image? (1)

rrohbeck (944847) | more than 3 years ago | (#35129960)

And even if that doesn't help it'll be easy to design a filter that removes the spatial frequencies they use. Or a small median filter.

I sense an announcement coming tomorrow... (1)

jeffmeden (135043) | more than 3 years ago | (#35127788)

"New Technique For Making Copy-Evident JPEG Images no longer Copy-Evident"

Seriously, I didnt sit in on the JPEG meetings or anything but it seems like this is a clever idea that could be so very easily circumvented. Recompress the picture, identify the regions exhibiting a "high frequency pattern" (which should be evident) and reverse the frequency of those pixels in the original file prior to recompressing.

Re:I sense an announcement coming tomorrow... (0)

Anonymous Coward | more than 3 years ago | (#35129698)

durrrrrrr
geordi: maybe we can reverse the polarity of the phase of the fourier transform of the energy spectrum on the pixel lattice manifold.
data: i can use my neural network to provide a bayesian prediction for what the data was before the klingons fucked it up

Uh oh (1)

JackSpratts (660957) | more than 3 years ago | (#35127800)

geez i hope they don't do this to movies. it will sabotage all those netflix dvds i "tivo to my harddrive" for "research purposes."

Introduced upon recompression, so... (1)

jameson (54982) | more than 3 years ago | (#35127804)

...just make sure you save as png, not jpeg.

Re:Introduced upon recompression, so... (1)

jameson (54982) | more than 3 years ago | (#35127826)

On second thought, someone else could re-encode as jpeg. So you may want to resize and perhaps blur a little. Either way I don't see why this wouldn't be trivial to defeat.

Doesn't Work (4, Informative)

nattt (568106) | more than 3 years ago | (#35127930)

So I downloaded their test image here: http://www.cl.cam.ac.uk/~abl26/copy-google.jpg [cam.ac.uk] that they claim gets a message on it when compressed by google proxy http://www.google.com/gwt/x/i?u=http%3A%2F%2Fwww.cl.cam.ac.uk/~abl26/copy-google.jpg&wsi=223e8e5df695e99c&ei=6ixQTebOCoPoxQW8rYlv&wsc=yq&whp=012e012f72be [google.com]

But when I take the original and re-save it in Photoshop CS5 I don't see the void lettering. I reduced the JPEG quality and kept trying and at quality 1, the lowest setting I was starting to see a pattern, but no words appeared.

I'd say their idea is nice, but doomed to failure, not least they mention "If you can’t see the message in the recompressed image, make sure your browser is rendering the images without scaling or filtering." which would be the obvious source of attack on such a method should it actually work in practise.

Re:Doesn't Work (1)

bluefoxlucid (723572) | more than 3 years ago | (#35128124)

I think the idea is there's some method for taking a munged picture and going, "Watch, I'll run an algorithm and... oh, look, a message with a hole cut in it where your ex-girlfriend's head is sucking that black man's cock..."

Re:Doesn't Work (3, Informative)

marcansoft (727665) | more than 3 years ago | (#35128256)

Apparently it only works at very specific quality settings. Re-saving with GIMP, I can see the message at quality 24, 38, 41 (barely), 43, 60, 65 (barely), 69 (barely), 72 (barely), and a few others even less.

As far as I can tell (I haven't read the paper), it works by setting up a static hard to compress pattern, and then slightly altering that pattern in certain macroblocks so that they just push the boundary into a different kind of compression artifact at certain quality/quantizer levels. So the entire image is compressed one way at one quality, a different way at another quality, and at the threshold between them there's a quality level where the message blocks compress differently and you can see them.

Also, recompressing has a high chance of destroying the effect permanently. For example, saving at quality 51 destroys the message, and re-compressing at any quality level no longer makes it visible.

Re:Doesn't Work (2)

daremonai (859175) | more than 3 years ago | (#35128424)

I tried it with gimp and it worked. Open the image, save at 60% quality, and the VOID is quite visible. Perhaps it's libjpeg's compression they're relying on. (I assume that's what gimp uses; I haven't actually checked.)

However, the method is easily defeated. Open the image, scale it to twice its size, then scale back down to the original size, and save at 60%. No watermark appears.

Re:Doesn't Work (0)

Anonymous Coward | more than 3 years ago | (#35128962)

So I downloaded their test image here: http://www.cl.cam.ac.uk/~abl26/copy-google.jpg [cam.ac.uk] that they claim gets a message on it when compressed by google proxy http://www.google.com/gwt/x/i?u=http%3A%2F%2Fwww.cl.cam.ac.uk/~abl26/copy-google.jpg&wsi=223e8e5df695e99c&ei=6ixQTebOCoPoxQW8rYlv&wsc=yq&whp=012e012f72be [google.com]

But when I take the original and re-save it in Photoshop CS5 I don't see the void lettering. I reduced the JPEG quality and kept trying and at quality 1, the lowest setting I was starting to see a pattern, but no words appeared.

I'd say their idea is nice, but doomed to failure, not least they mention "If you can’t see the message in the recompressed image, make sure your browser is rendering the images without scaling or filtering." which would be the obvious source of attack on such a method should it actually work in practise.

With Paint.NET, it is visible only at quality 60.

Re:Doesn't Work (1)

bouldin (828821) | more than 3 years ago | (#35129146)

I also tried recompressing the test image, and was only able to see the watermark around the 60-65 quality range for JPEG.

However, the goal presented in the paper is to provide a "targeted mark" that will be visible given a predictable recompression scheme. So, if you know a particular photo site (or WAP gateway) recompresses at 60, you can mark the picture to target quality rating of 60.

The paper concludes with "untargeted marks" as a future research opportunity. The authors describe an untargeted mark as one that would appear with some degree of certainty without knowing the recompression parameters of site X or WAP gateway Y.

As others have posted, there should be ways to recompress without the mark showing. Think of this technique as an exploit for JPEG quantization.. There will be workarounds to prevent the exploit.

Re:Doesn't Work (0)

Anonymous Coward | more than 3 years ago | (#35129582)

Perhaps it's just my monitor settings, but I can see the VOID lettering in the original test image without re-compressing it.

Easily defeated (1)

wiredlogic (135348) | more than 3 years ago | (#35128104)

As usual this can be easily defeated by re-sampling or noise filtering. If you're targeting web media and have a high enough resolution source image then you have plenty of redundant pixels to play with to wipe out the watermark.

A better solution for authenticity verification would be digitally signed checksums.

Our algorithm works by adding a high-frequency pattern to the image with an amplitude carefully selected to cause maximum quantization error on recompression at a chosen target JPEG quality factor. The amplitude is modulated with a covert warning message, so that foreground message blocks experience maximum quantization error in the opposite direction to background message blocks. While the message is invisible in the marked original image, it becomes visible due to clipping in a recompressed copy,

This has very limited utility (1)

davidwr (791652) | more than 3 years ago | (#35128150)

I can see this if your concern is a pre-canned compression such as a specific proxy run by someone that doesn't care if the images it produce appear "marked."

If the goal is to prevent end-users from re-scaling the image in an arbitrary way, it's not going to be very useful.

Protip (1)

SethThresher (1958152) | more than 3 years ago | (#35128152)

This is why I ALWAYS do all of my drunken photo editing in .png!

This is nothing new (1)

mathimus1863 (1120437) | more than 3 years ago | (#35128192)

My job is image processing, and we are all well aware of the "quirks" of storing images as JPEG. Since it typically uses frequency information, converting to a BMP for a photo editor, and then converting back with some minor modifications introduces all sorts of artifacts into the JPEG coefficients upon recompression. These artifacts can be detected by a program looking for them, and I'm surprised such algorithms are not in use in existing software. And the detection would be able to ignore image resizing...

Of course, this kind of detection can be evaded by someone who understands the compression algorithms and knows how to work around it... but at least it could flag images modified by amateurs. After all, the TFA has the same goal, just it wants to make the "flag" be user-visible, not just rely on a program for detecting and flagging it.

Irrelevant! (1)

hockeygeek (192147) | more than 3 years ago | (#35128226)

Completely irrelevant tech. I've seen a few photoshops in my time, and I can tell by the pixels whether it's photoshopped or not....

Re:Irrelevant! (1)

$RANDOMLUSER (804576) | more than 3 years ago | (#35128292)

ISWYDT

Drunken Sex Party Photos (1)

E. Edward Grey (815075) | more than 3 years ago | (#35128238)

I think you'll find that when it comes to Drunken Sex Party Photos, most of us who are going out of our way to look at them really don't care whether or not they have been edited.

Digital Signature (1)

nuckfuts (690967) | more than 3 years ago | (#35128244)

Knowing whether a photo or video has been digitally altered is important for images used as legal evidence. I would not be surprised to see makers of digital cameras and editing software embed a digital signature that can be used to detect alteration. Perhaps with software like Photoshop, it might even record what types of modification were done. There would be little reason to mistrust a photo that was merely rescaled, for example.

Keep in mind that some digital technology already embeds data to prevent counterfeiting [pcworld.com] .

Re:Digital Signature (1)

Rich0 (548339) | more than 3 years ago | (#35129186)

Many higher-end cameras do in fact include technology to authenticate original photos. I cannot vouch for how well-implemented they are.

However, all of them are susceptible to the DRM weakness - the guy with the camera has physical possession of everything necessary to generate a faked photo, including the keys. Sure, the keys might be locked up in some chip where they are theoretically difficult to access. However, they are still vulnerable to interception. If you extract the keys then you can make any picture you want "authentic."

With software like photoshop the DRM weakness is much greater, since now we're talking software-level attacks instead of hardware attacks. The only way this would work is if the entire chain from hardware to bios to OS to software uses a trusted boot chain with keys in a TPM module or whatever, and no point along the chain contains a vulnerability. The chances of that ever happening down to the level of an app like Photoshop are pretty slim.

Re:Digital Signature (1)

sxeraverx (962068) | more than 3 years ago | (#35129280)

Except that if such information is stored with the photo, it can by definition be altered when the photo is altered.

Re:Digital Signature (1)

nuckfuts (690967) | more than 3 years ago | (#35129344)

You can alter whatever you want, but without the manufacturer's private key [wikipedia.org] , you can't digitally sign the result.

Re:Digital Signature (0)

Anonymous Coward | more than 3 years ago | (#35130186)

Except that if such information is stored with the photo, it can by definition be altered when the photo is altered.

Which of course will cause the digital signature check to fail indicating the photo has been tampered with... unless you have access to the secret key when doing the alterations like Rich0 said.

Re:Digital Signature (1)

lgw (121541) | more than 3 years ago | (#35129308)

That would only make it hard to alter digital photographs by someone who did not have access to the camera (since the camera must contain the signing key), which doesn't help any in a legal chain-of-custody question. Unless the signing was done by a FIPS140-2 level 4 component, and those are remarkably expensive - but then for a special purpose forensic camera, it would make a lot of sense.

nice theory, not practical (1)

Zappy (7013) | more than 3 years ago | (#35128250)

They where not kidding about the specific quality settings. I tried it with the demo image and and The Gimp to reveal the message. I was only able to have it appear only remotely recognizable at 3 of the 101 quality setting

Doesn't work too well in Paint Shop Pro 5 (0)

Anonymous Coward | more than 3 years ago | (#35128302)

Recompress the example image in PSP5, and you'll only get the "VOID" using a compression rate around 50%, too high and all you'll get is a pattern of dots, too low and all you'll get is a very faint grid pattern

This technique may stop photoshoppers, but it won't stop paintshoppers! :D

Oh no! (1)

SnarfQuest (469614) | more than 3 years ago | (#35128384)

"The days of wondering whether those drunken sex party photos are indeed the Olsen Twins, or if they are just the Mary-Kate and Ashley's faces photo-shopped on the bodies of Lindsay Lohan and Amy Winehouse are OVER!"

You mean that poster next to my Olsen Twin poster is a fake? (Rushes off, and rips a poster off the wall).

I bet you can't guess which poster I removed!

Target Quality Factor (1)

thehickcoder (620326) | more than 3 years ago | (#35128594)

Our algorithm works by adding a high-frequency pattern to the image with an amplitude carefully selected to cause maximum quantization error on recompression at a chosen target JPEG quality factor.

The key here is JPEG quality factor. This only works on a specific quality factor. Just pick a different one. I just tried it using their example image. At some quality factors you can see somthing funny going on (spots on image). But, at any factor you would use to actually compress a photo (above 90) the image looks fine.
This could work for the bandwith-saving proxy mentioned in the article since they will have low quality factors. But what would be the point then? Mangling images when viewed on a cellphone?

Why you gotta insult Lindsay? (0)

elrous0 (869638) | more than 3 years ago | (#35128620)

You know, it's not her fault that her fame-whoring parents pushed her into the kind of child stardom that would leave anyone at least a little warped. It's not her fault that too much fame too fast led to a parade of leeches and "friends" who were all-too-happy to feed her addictions while using her for their own ends. It's not her fault that paparazzi follow her everywhere just waiting for her to make the slightest mistake so they can get a picture of it and make money.

How many of you wouldn't have ended up in the exact same straights (or worse) if that had been YOUR life?

Re:Why you gotta insult Lindsay? (1)

Minwee (522556) | more than 3 years ago | (#35128886)

How many of you wouldn't have ended up in the exact same straights (or worse) if that had been YOUR life?

Through it all, at least Lindsay knows how to spell straits [thefreedictionary.com] .

MD5 (0)

Anonymous Coward | more than 3 years ago | (#35128626)

If you want to be able to detect whether one JPG file is different from another one, can't you just write down the MD5 hash of the original?

Save As... (1)

Adrian Lopez (2615) | more than 3 years ago | (#35128852)

I-Swear-It-Is-Real.PNG

Arnold Schwartenegger's and Martin Sheen's heads (1)

PolygamousRanchKid (1290638) | more than 3 years ago | (#35129012)

Olsen Twins, or if they are just the Mary-Kate and Ashley's faces photo-shopped on the bodies of Lindsay Lohan and Amy Winehouse

It would be more amusing to really transform the heads of Arnold Schwartenegger's and Martin Sheen's onto bodies Lindsay Lohan and Amy Winehouse.

Plastic surgeons in California can do that with Botox, can't they?

The cops would be too afraid to arrest a Arnold Schwartenegger headed Lindsay Lohoan. Poor Martin Sheen headed Amy Winehouse would hear from the traffic cops:

"I'm sorry Mr. Sheen, but are those two and a half double D's on your chest?"

In today's world? That will never work. (0)

Anonymous Coward | more than 3 years ago | (#35129134)

How's that going to stop people from print screening the jpeg into a bmp, modifying the bitmap, and then recompressing it as a jpeg?

What does this do to my scroll wheel? (1)

killmenow (184444) | more than 3 years ago | (#35129144)

1. See interesting but slightly too small pic on web page
2. scroll wheel to zoom the page
3. IMAGE NO LONGER VIEWABLE BECAUSE ASSHATS ARE AFRAID YOU'LL COPY IT.

Useless (1)

sskagent (1170913) | more than 3 years ago | (#35129152)

This thread is useless without pictures.

obvious work around? (0)

Anonymous Coward | more than 3 years ago | (#35129282)

What if I just take a screen shot? Hit print screen and work with that image? I could even stitch a few together if the picture was larger than my monitors resolution.

I Tested - It's Useless (1)

sexconker (1179573) | more than 3 years ago | (#35129510)

Their sample image is here: http://www.cl.cam.ac.uk/~abl26/copy-background.jpg [cam.ac.uk]
Their sample image after recompressing is here: http://www.cl.cam.ac.uk/~abl26/copy-background-recomp.jpg [cam.ac.uk]
According to them, the sample recompressed image is saved "with particular quality settings".

So I opened the original image file in GIMP, went to save it as a JPEG, made sure the preview was turned on, and saw nothing.
Of course, this is because I save every jpeg at 1x1, floating point, 100 quality.

So I reduced the quality. After a while, the image appears. A change of 1% (from "82" to "83", for example) can render the message completely visible, and another change can render it completely invisible.

I did a low strength blur (imperceptible to my eyes) on the image, and went through the same experiment, and the message was rendered completely gone.
I suspect that same could be done by adding a small amount of noise, etc.

Yawn.

What about websites with non-viewable images? (1)

k6mfw (1182893) | more than 3 years ago | (#35129924)

No joke, I've noticed a trend where more and more sites have these javascript or some other such crap to display the image. They begin with a insy tinsy image, when you click it shows enlargement but resolution is not great (and of course the right button and various commands are disabled). It is not that I will pirate images but it pains me to no end when I find a fantastic photo of i.e. Gina Lollobrigida (in one her beautiful dresses from "Beautiful But Dangerous" or "Fast and Sexy") and I want to save it because most likely that website has a limited lifespan! So far screen grabs (i.e. PrtScn or cmd-shift-3) still work.... but I wonder how much longer. Will it come a time when having to use a camera like what they did for "screen grabs" in the 20th century?

Regarding non-viewable images, if concerned of someone stealing an image, don't have images. Believe it our not, there are people with this kind of mentality. Like someone who takes a lot of photos at a convention or a fair but doesn't release the images out of fear someone will "steal" their photos. They argue that some of these photos may become pulitzer prize photos or incredible money shots. But hey, if they expect to get high monetary value photos at usual public events of various ordinary people, they are in the wrong place. Need to be with paparazzi types following Madonna or Britney Spears.

If there is a watermark...there is a way to patch (1)

Maxo-Texas (864189) | more than 3 years ago | (#35130036)

If you know the watermark technique, then you can erase the original watermark and write a new unified watermark.

In fakes (including Tron 2), the main issue is that the lighting is never right.

In reality, the mouse cable is reflecting dark grey light at you. Each key on the keyboard is reflecting a mixture of black and and white at you. The screen is shining orange, green, blue, large masses of white, and grey on you.

If the person next to you has a blue dress, that blue is reflecting off you.

It's unholy ridiculously complicated and all they can do is "model" it and get close.

But it looks fake.

I was thinking for Tron 2, they should have had the young actor standing in for bridges (who had dots on his face) should have had white face makeup which would pick up the real room lighting and that could be used to adjust the lighting on the simulated young jeff face.

NOTICE: This looks shopped! (2)

da3dAlus (20553) | more than 3 years ago | (#35130154)

I can tell from some of the pixels and from seeing a few shops in my time. What, are they borrowing an algorithm from 4chan?
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