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A warning to anyone trying to pass off faked photos as real: Hany Farid is on to you. The Dartmouth College computer scientist is developing digital forensics software that can instantly tell whether an image has been manipulated, and what make and model of camera captured it. It's "exactly like gun ballistics," says Farid, 44. "If Photoshop touches that image, we will know about it."
Much as a rifle barrel imprints a unique pattern of grooves on bullets, digital cameras have electronic signatures—minute variations of resolution and image compression in the images they produce. Farid and his students received permission from photo-sharing site Flickr to download millions of images and build a signature database of every one of the 10,000-plus digital camera models ever made. To verify a picture, Farid's system checks it against that database to identify the equipment used. It then looks for any variations in the signature, which would indicate fakery. If the system finds traces of Adobe Photoshop (ADBE), which also leaves a signature (and is the most common image manipulation program), that's a sure sign of picture alteration.
Farid plans to sell his software, though he hasn't decided whether to start his own company or partner with Adobe, which is helping to develop the technology. The program may be useful to law enforcement agencies that need unaltered photographs for court evidence, says Stephen A. Saltzburg, a law professor at George Washington University. Newspapers might use it to determine the authenticity of freelance photos. People will inevitably try to outsmart the program, "but we're going to make it pretty hard for them," says Farid. "You're going to have to work. And right now, you don't have to work."
Farid initially didn't want anything to do with the photo business. As the son of an Eastman Kodak (EK) chemist, he says he wanted to cut his own career path. In college, his mother persuaded him to take a class in computers after Time declared them "Machine of the Year" for 1982. Farid says he tried so hard to steer clear of the profession of his now-retired father that "I apparently ran in a circle," and by 1999 he was working in digital imaging.
One limitation of Farid's technology: It only shows that an image has been doctored. Figuring out what was altered, and how, requires other techniques. Farid uses 3D modeling software that determines whether the shadows in a photo all come from consistent light sources. If the shadows fall at impossible angles, the shot is probably a composite of multiple images. In a 2009 paper, he applied this technique to a picture of Lee Harvey Oswald long thought to be phony. Farid concluded the photo was real, outraging Kennedy assassination conspiracy theorists. "I wanted the photo to be fake. That would have been such a cooler result," he says. "Now people think I'm part of the conspiracy."
Photoshop is so good, it's hard to tell whether an image is faked
Locating digital signatures left by cameras
Farid's father was a chemist at Eastman Kodak