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Debunking Photoshop Fakery
December 12, 2004 NYTimes.com Magazine

By RYAN BIGGE

Our faith in photography has been forever compromised by computer programs like Photoshop that doctor images with a relatively high degree of ease and verisimilitude. When you come across a provocative photo on the Web -- John Kerry and Jane Fonda protesting together, say -- it can be hard to know what to make of it.

But not for Hany Farid. In May, Farid, a professor of computer science at Dartmouth College, unveiled software that helps determine whether a digital image has been tampered with. Much as art experts detect forgeries by studying the minutia of brush strokes, Farid has devised methods of analyzing the clusters of pixels that make up a digital photo. After crunching the numbers, his program generates a map of the suspect image that
calls attention to suspicious areas where tampering may have occurred.

Here's how it works. Each pixel in a photo represents a small piece of coded information, and Farid's program looks for patterns of information within the overall composition of the photo. Unaltered images, he discovered, tend to have what you might call naturally occurring patterns of information. Images that have been altered, by contrast, tend to have abnormal patterns of information that, while invisible to the eye, are detectable by computer. Making things easier, most doctored images are produced with common manipulations -- like resizing, duplication, adjusting the contrast and airbrushing.

Farid began thinking about how to authenticate digital imagery after discovering that photos taken with a digital camera could be considered admissible evidence in United States courts. As a pioneer in this type of forensic analysis, he receives numerous unsolicited e-mail messages from Photoshop-fraud victims, including one from a Brazilian model who claimed Budweiser spliced her head onto the body of another woman in a print ad. "You gotta love this job if you've got supermodels calling you," Farid says.