There should be only one person in the photo. Face recognition accuracy depends on the quality of a face image. The system detects the face and creates a major facial pattern.
Ever see an attractive person and wonder what he or she looked like naked? Two porn websites have made that fantasy a reality, using facial-recognition technology to match user-submitted photos of people to porn stars. But there doesn't appear to be any mechanism for consent on the part of the people whose images are submitted. And what happens if someone uses the matches to harass an ex-girlfriend, an ex-husband or a friend's mother?