Digital Photos: Seeing Shouldn't Always Lead to Believing

By Matthew Harwood

In a fascinating article for Scientific American, digital forensics expert Hany Farid explores the societal implications of doctored digital images.

At any fine electronic retailer, people can now buy powerful software programs that allow users to doctor an image, and in a sense, alter reality. Normally, the software is used for legitimate or benign reasons, making a cloudy day into a clear day, but it has also been abused.

A recent example is the case of photographer Liu Weiqing, who won awards for his photo of endangered antelopes unperturbed by a passing high speed train, which originally ran in hundreds of Chinese newspapers. The picture, however, was exposed as a fraud. Lui had stitched two images together to produce his desired result.

Although it may not immediately apparent, fradulent digital images can have dire consequences for everything from science to politics to the law.

As Farid writes:

The validity of an image can determine whether or not someone goes to prison and whether a claimed scientific discovery is a revolutionary advance or a craven deception that will leave a dark stain on the entire field. Fake images can sway elections, as is thought to have happened with the electoral defeat of Senator Millard E. Tydings in 1950, after a doctored picture was released showing him talking with Earl Browder, the leader of the American Communist Party. Political ads in recent years have seen a startling number of doctored photographs, such as a faux newspaper clipping distributed on the Internet in early 2004 that purported to show John Kerry on stage with Jane Fonda at a 1970s Vietnam War protest. More than ever before, it is important to know when seeing can be believing.

The law has had a hard time with doctored digital images, especially in court, when a jury or an expert has to determine whether a digital photo is real or fake. The ever increasing sophistication of computer-generated images has led many state and federal courts to say juries should not be made to choose which ones are real and which ones have been doctored. One federal judge, according to Farid, has even questioned whether expert witnesses can make the correct determination.

Farid says there are five techniques that can restore trust in digital photographs. (To view them, click here.) Digital forensic technicians have developed these by understanding the statistical and geometric properties of an image and how tampering effects an image. An algorithm is then used to uncover the irregularities tampering produces. Increasingly, scientific publishers, the media, and the courts are adopting them. Nevertheless, he says digital forensic experts are in an "arms race" with fakers and frauds.

"The field of image forensics will, however, continue to make it harder and more time-consuming (but never impossible) to create a forgery that cannot be detected," says Farid.


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