Kristina at Science News writes "A new way to process images reveals an extrasolar planet that had been hiding in an 11-year-old Hubble picture. After ground-based telescopes found three planets orbiting the young star HR 8799, a team took that information and reprocessed some 11-year-old Hubble Space Telescope images. Voila. There was one of the three planets, captured by Hubble but not visible until new knowledge could see the picture in a fresh light. The technique could reveal hidden treasures in many archived telescope images."
For reference, the first exoplanet to be (knowingly) directly imaged was 2M1207_b in late 2004.