I've never played with fingerprinting per se, but long ago I did write a program to detect near-duplicate images. It was based on comparing square of the diffe

I've never played with fingerprinting per se, but long ago I did write a program to detect near-duplicate images. It was based on comparing square of the differences of extremely downscaled images. Quite good at it's intended purpose, exposed the fact that a few images were photoshops and revealed that images that were inherently low-contrast could easily be confused by that approach--beaches looked an awful lot like beaches.