New technique can link individual images with the camera that took them

Researchers at a US university have developed a process that can accurately link digital images to the camera with which they were taken.

The team from Binghamton University in New York claimed that the system allows the identification of a camera in much the same way that tell-tale scratches are used by forensic examiners to identify the gun from which a bullet was fired.

The process could have several applications, according to the academics, including bringing child pornographers to justice.

"The defence in these kind of cases would often be that the images were not taken by this person's camera, or that the images are not of real children," said Jessica Fridrich, associate professor of electrical and computer engineering at Binghamton University.

"But if it can be shown that the original images were taken by the person's mobile phone or camera, it becomes a much stronger case than just a bunch of digital images that we all know are notoriously easy to manipulate."

Fridrich and two members of her research team, Jan Lukas and Miroslav Goljan, are co-inventors of the technique, which can also be used to detect forged images.

The trio have applied for two patents related to the technique, which provides the most robust strategy for digital image forgery detection to date.

The process is rooted in the discovery by her research group that every original digital picture is overlaid by a weak noise-like pattern of pixel-to-pixel non-uniformity.

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

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 developed by Fridrich and her co-inventors can be used to provide important information about the origins and authenticity of a single image.

The limitation of the technique is that it requires either the camera or multiple images taken by the same camera, and is not informative if only a single image is available for analysis.

In preliminary tests, Fridrich's lab analysed 2,700 pictures taken by nine digital cameras and linked individual images with the camera that took them with 100 per cent accuracy.

"We already know that law enforcement wants to be able to use this," said Fridrich. "What we have right now is a research tool, a raw technology that we will continue to improve."