Try the new Google Image Labeler. It’s a little tool Google has put together to get you to label images, and help improve their image search. But they’ve done two very clever things: firstly, you have to label the image at the same time as a randomly-selected partner, and only if both you and your partner select the same label will it count. Secondly, they’ve made it into a game, so that the pair that scores the most matching labels appears on a leaderboard. Also, after the game you can check what labels your partner gave by hovering over the thumbnails. It’s interesting to see what other people make of the same image, and the game weirdly addictive. Give it a go.