With all the attention these days on NSA activities, it's easy to forget that much surveillance in the United States takes place at the state and local level, and it is also regulated by state and local law. Much of the really high tech stuff is centralized in the federal government's hands, but debate about at least one new technology—facial recognition—is going on in some places at the state level, and that's a good thing.
Most facial recognition technology works by identifying various distinguishing features and measurements of an individual human face in an image and comparing them to images stored in a large database of pictures matched with other data (say, for instance, all passport or driver's license photos or all pictures stored in a social network application). Especially if linked up with proliferating camera systems and postings of pictures online, this is a powerful identification tool, and not just for detecting or recognizing suspects but for ID-ing those with whom they associate. Those who worry about the government looking through your call records should probably worry about it looking through your pictures, too.