The Sony eyetoy was a digital camera for the Playstation 2 which could process images and detect motion, allowing players to interact with games. At thwe time of release, the eyetoy was revolutionary, as this kind of technology had not been released before, but it has since gone out of fashion.
The Eyetoy Play game series was released at the same time, which contains a variety of games where players interact with things on the screen, such as washing windows with your hands and boxing a virtual opponent. The Eyetoy also functions as a webcam for your computer, which means it is still useful to have lying around even though better camera technology has since been released.
The Eyetoy and the games that use it are great fun to play, and the picture quality is reasonably good. It is compatible with the Playstation 3, but the more recent Playstation Eye has better picture quality and more features.