The Null Device
Researchers at Binghamton University have developed a method of identifying the digital camera that took a particular image by isolating the unique noise fingerprint of the camera's sensor:
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.The researchers are promoting the development as a tool for catching and prosecuting child pornographers, though it could have other applications. For example, had the British government a database of the fingerprints of all digital cameras sold in the UK, correlated to the ID card numbers of the purchasers, they could quite easily arrest underground artists such as Banksy just by analysing the images on their web sites. During the Cold War, the KGB and East German Stasi had copies of all the letters typed on each typewriter in the country, so they could identify which typewriter a piece of samizdat came from. It is not inconceivable, in the Homeland Security Age, that an agreement will be worked out with camera manufacturers to supply the government with sensor fingerprint data (which could be taken in the factory during the testing phase) correlated with serial numbers; then all that would be necessary would be a law requiring camera purchases to be registered against identification. (In Australia, where you have to show ID for sending mail overseas, and where everyone is too relaxed and laid-back to care about civil liberties, such a law would sail through Parliament with bipartisan support and next to no debate; in Britain, those pesky Lords would probably cause trouble, for a while, at least.)
Of course, as Ars Technica states, it will only be a matter of time before software exists for removing or obfuscating camera fingerprints, or indeed for adding someone else's fingerprint to an image, rendering the process somewhat less than useful.