Google released this thing known as Google Image Labeler, it basically pins user vs. user to label images from Google images. The way you score points is if you both label the image with the same label.
Here is my live demo of it in action (should be live soon):
How does it work?
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.
The game is somewhat addictive, especially if the one you are partnered with is as quick as you are.
This is a great way for Google to label their images in a short amount of time.
Danny has a huge write up on it in a deeper sense named Google Images Labeler: Google's Challenge To Flickr?
Pretty cool stuff.