Just as ballistic experts can trace bullet casings back to the gun that fired the shell, university researchers have devised a way to trace specific digital photographs back to the exact digital camera that took the photo.

Every original digital picture is overlaid by a weak noiselike pattern of pixel-to-pixel nonuniformity, according to Jessica Fridrich, an associate professor of electrical and computer engineering at Binghamton University, State University of New York.

Although these patterns are invisible to the human eye, the unique reference pattern or “fingerprint” of any camera can be electronically extractedby analyzing a number of images taken by a single camera.

“This technique can provide a proof that a given digital image came from a specific digital still or video camera,” Fridrich said. Thus, whenever a digital image is associated with a crime – such as child pornography or movie piracy –investigators can now provide crucial evidence linking those images to specific cameras.

An example of the ‘noise’ researchers believe to be unique to each digital camera, allowing digital images to be linked to the precise camera that shot the photograph. (Binghamton University photo.)

Fridrich said that means that as long as examiners have either the camera that took the image or multiple images they know were taken by the same camera, an algorithm she developed can extract and define the camera’s unique pattern of pixel-to-pixel nonuniformity.