EyeToy: Play is a video game for the PlayStation 2, released in 2003. It was the first game to make use of the PlayStation 2's video camera accessory, EyeToy. The game was initially packaged with the EyeToy when the accessory was first released. It features twelve mini-games to choose from. This game, and all other EyeToy titles, are played by moving one's body. The motion is detected by the USB camera. The software recognizes pixel changes in the video image and compares the proximity of the change to other game objects to play the game. Users who get a high score get to take a photo to tease other players.
Source: Wikipedia, "EyeToy: Play", available under the CC-BY-SA License.