Digital Image Forensics

As the ability to manipulate digital image media becomes more common, our understanding of technological, ethical and legal implications is lagging. At the General Meeting in April, Prof. Hany Farid of Dartmouth College discussed some of these issues and described computational techniques which have been developed for detecting such tampering. Operating in the absence of digital watermarks or signatures, these techniques quantify and detect statisical, optical and geometric correlations that result from specific forms of digital tampering.

  With $100 Photoshop software and a little training, computer users can drastically alter digital photos, shedding a few pounds from a high school prom picture or removing a tumor from a medical image. While manipulated photos can be very difficult to detect, Hany Farid, associate chair of the computer science department at Dartmouth, is one of the first people to develop a method to find alterations in digital photographs.

Farid is a founder of the emerging field of digital forensics, which uses computer software to detect statistical differences in a photograph’s lighting, light reflections in eyes and other abnormalities that indicate that a photo has been altered. Detecting alterations is far more expensive and time consuming than altering a photograph, Farid said. Farid typically charges between $5,000 and $25,000 for his services and operators must be highly trained to use his software, he said.

“There is no magic bullet. It’s not simple,” he said.

After eight years of research and development, Farid delivered the first public digital forensics software to the Federal Bureau of Investigations last month. Law enforcement agencies provided some of the largest grants for Farid’s research as these agencies need a scientific method to determine if a photograph has been doctored for trials, he said.

Digital forensics has been especially important for child pornography cases since the Supreme Court ruled that digitally generated child pornography on the internet is protected as a form of free speech, Farid said. In his opinion, computer technology is not advanced enough to create a digital child that is indistinguishable from a real child by the naked eye, although in 10 to 15 years this could change. Many defense attorneys, however, claim that the children in digital pornography were computer generated to instill reasonable doubt in juries. Prosecutors have called on Farid several times to determine if images were digitally created.

The media is another potential market for digital forensics, he said. Reuters was recently faulted after one its photographers photo-shopped smoke on to a picture of bombed building in Beirut during the 2006 Lebanon-Israeli conflict and Newsweek was criticized for superimposing Martha Stewart’s head onto a model’s body for its cover.

Hany Farid received his Ph.D. in Computer Science from the University of Pennsylvania. Following a two-year post-doctoral position in Brain and Cognitive Sciences at MIT, he joined the Dartmouth faculty.

From working with federal law enforcement agencies on digital forensics to the reconstruction of ancient Egyptian tombs, Hany works and plays with digital media at the crossroads of computer science, engineering, mathematics, optics and psychology.