Tagging picture is sometimes not very funny, but if you turn this into a two-player game. you will get Google Image Labeler: on a random principle, a partner is found by Google Image Labeler. If your partner suggests the same words or definitions for a displayed image, you will win points. Of course the more precise you are, the more points you will win. It's worse to try, believe me! This game is highly addictive! http://images.google.com/imagelabeler/
And of course if you want so more background information concerning this "game", read this interesting Wiki Article : http://en.wikipedia.org/wiki/Google_Image_Labeler
Here are other websites of ESP Games (http://en.wikipedia.org/wiki/ESP_Game) : gwap.com with the possibility to tag tunes (!) or you also have PeekaBoom.org which also makes a lot of fun to play with.
