Wednesday, December 29, 2010

Raising the bar a little higher

Hany Farid vs. Photoshop
The Dartmouth computer scientist and forensic imaging specialist has come up with a way to tell whether a digital photograph is authentic

"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 ..."

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