Virginia Beach has implemented a face recognition system that searches for wanted felons and missing persons. The primary criterion for detection is distance between dominant features of the face -- e.g., space between eyes, or between the tip of your nose and your chin.
Apparently, there is no permanent archive of recorded images. If the system finds no match for a particular face, the image is discarded.
Virginia Beach has been on the air since September. So far, no one has been arrested or found.
Coverage is here.