Go to http://images.google.com/imagelabeler/ and login if you have a google account to change your nick or you can just start as guest. You will be randomly paired with someone and you will get a timer. You will get random images and you will have to write words to label them. For instance if you see a n elephant you have to write things such as: elephant, animal, africa, etc. Once one of your words matches one of your pair, you get a new image. The more matches, the higher score.