Google Image Labeler is new feature of Google Image Search that allows you to label random images to help improve the quality of Google’s image search results. You’ll be randomly paired with a partner who’s online and using the feature. Over a 90-second period, you and your partner will be shown the same set of images and asked to provide as many labels as possible to describe each image you see. When your label matches your partner’s label, you’ll earn some points and move on to the next image until time runs out. After time expires, you can explore the images you’ve seen and the websites where those images were found. And we’ll show you the points you’ve earned throughout the session. Link : hxxp://images.google.com/imagelabeler/
I think it's just Google trying to make it fun for people to participate in what's a kind of survey. Instead of just telling people to describe the images, they make it a game to see who can do the best.