Alexa Wright, an artist, has developped something she calls "Alter Ego". (No link, 'cause the main page is down, but you can find lots of articles by googling "Alter Ego Alexa Wright"). It's a camera, computer and LCD setup so that initially when you stare into the LCD, it looks like you're staring into a mirror. However, if you move your face around enough (say by smiling, winking, etc.), the software on the computer will be able to recognize (because of the motion) that there is someone there, and then will try to do some facial analysis to determine what part of the image it's capturing is your eye, nose mouth, and so on. Once it gathers enough info, it'll map a texture representing your face onto a 3D model, and then start having your reflection behaving randomly. For example, you might suddenly see your reflection smile and talk to you (no sound though).