David Nishimura notes this Discovery News story on the development of cellphone technology that could help identify stolen art (mentioned earlier here):
"A cell phone picture could be worth a million dollars — particularly if it's a snapshot of a piece of stolen art.
"A new software tool plays detective by automatically comparing cell phone photos with images in a database of stolen art. The technology could help restore stolen goods to their rightful owners and solve the hundreds of art theft cases opened each year in the United States alone.
"For now, the system works on paintings, carpets and coins, but the researchers already have plans to go beyond those.
"'Extensions are on the way to make the system suitable for thee-dimensional objects. These extensions will cover sculptures as well as three-dimensional objects in general,' said Bertram Nickolay, head of the department Security Technology at the Fraunhofer Institute in Berlin, Germany."
"Sounds like a pretty simple and practicable idea, patching together well-established technologies. Take a database of images of stolen artworks, and search it using other images and a pattern-matching application. You'll end up with some false positives, of course, but as long as the matching algorithm is reasonably sophisticated, you should still have a useful tool for flagging possible problem paintings for further investigation."
UPDATE: Derek Fincham also likes the idea, but says "the problem of course is which database to check. At present there are a number of different theft databases. The largest and most successful is the Art Loss Register. However that site is not accessible to the public at large. You have to pay for and request the ALR to conduct its own search of its data. ... [A]s I've argued before, the first company which figures out how to make a simple, universal and easy-to-use database will really stand out, and will also really help to legitimize the art and antiquities trade generally. Until such a database exists though, we will continue to see good faith purchasers buying stolen or illicitly excavated works leading to the classic art law dispute between an original owner and a good faith purchaser."