Boing Boing: Digital cameras have unique "noise" fingerprints?:

Like actual fingerprints, the digital "noise" in original images is stochastic in nature - that is, it contains random variables - which are inevitably created during the manufacturing process of the camera and its sensors. This virtually ensures that the noise imposed on the digital images from any particular camera will be consistent from one image to the next, even while it is distinctly different.

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

My gibbering libertarian side doesn't really like this, since I know how it will end up being used. My inner-realist knew it was inevitable. My geek-side thinks this is really cool tech.