Link from Binghamton University in New York:

...a stunning new technology in development at Binghamton University, State University of New York, that can reliably link digital images to the camera with which they were taken, in much the same way that tell-tale scratches are used by forensic examiners to link bullets to the gun that fired them.
This would allow forensic examiners to link digital images to digital cameras, by examining a form of noise in the images that resembles a fingerprint. There are some limitations, the examiner would have to have multiple other images taken by the camera to compare with, or understandably, the camera itself.

Other interesting points in the article include:

...the absence of the expected digital fingerprint in any portion of an image that provides the most conclusive evidence of image tampering.
In the near future, Fridrich's technique promises to find application in the analysis of scanned and video imagery. There it can be expected to make life more difficult for forgers, or any others whose criminal pursuits rely on the misuse of digital images.