Your tax dollars at work: the latest PC Magazine reports "Researchers at the U.S. Department of Energy's Idaho National Engineering and Environmental Laboratory have developed software that can detect extremely tiny differences -- smaller than a fraction of a pixel -- between two digital images...."
Update: PC Mag's description is wildly inaccurate. The INEEL "breakthrough" is a program that rapidly aligns two digital images and then alternates them on-screen, which causes non-matched pixels to flicker, at which point the human observer notes the differences rapidly. The real impressive part is that "The alignment compensates for differences in camera angle, height, zoom or other distractions that previously confounded flip-flop comparisons."