Thursday, July 22, 2004

Researchers attempt to develop software to authenticate digital photos

As a digital photographer myself, I was particularly interested in the methods being developed by researchers to authenticate digital images.

"It used to be that you had a photograph, and that was the end of it - that was truth," said Hany Farid, an associate professor of computer science at Dartmouth College who is a leader in the field. "We're trying to bring some of that back. To put some measure of guarantee back in photography."

Over the last three years, Professor Farid and his students have become experts at forgery, making hundreds of images that look authentic but have in fact been digitally tweaked. License plate numbers are changed. A single stool standing on a checkerboard floor is suddenly a pair of stools. Dents on a car are wiped away with a few mouse clicks.

The skillful tampering disturbed the images in ways that the human eye could not detect. But Professor Farid says his algorithms can spot them and sound the alarm.

Jessica Fridrich, a research professor in electrical and computer engineering at the State University of New York at Binghamton, is approaching the fraud problem from the other side. She is trying to figure out who took the digital picture in the first place.

Just like the rifling in a gun barrel leaves a distinctive pattern on the bullets it fires, a digital camera has a signature of sorts. Today's digital cameras have sensors with millions of pixels. In each camera, a small handful of these are either too bright or are burnt out entirely. When a camera takes a picture, the imperfections leave a unique pattern, Professor Fridrich has discovered in preliminary research.

Now, she is trying to embed a bit of the photographer in the picture, too. The patterns in the iris - the colored part of the eye - are at least as distinctive as a person's fingerprint. With money from the Air Force, Professor Fridrich is designing a camera that takes two pictures at once: one though the camera lens, and a smaller one of the photographe's iris. The iris image along with the time and place of the photo session would then be compressed, encrypted and instantly hidden within the larger picture just taken.
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