sciencehabit writes Appear in a photo taken at a protest march, a gay bar, or an abortion clinic, and your friends might recognize you. But a machine probably won't — at least for now. Unless a computer has been tasked to look for you, has trained on dozens of photos of your face, and has high-quality images to examine, your anonymity is safe. Nor is it yet possible for a computer to scour the Internet and find you in random, uncaptioned photos. But within the walled garden of Facebook, which contains by far the largest collection of personal photographs in the world, the technology for doing all that is beginning to blossom.