He's set up an online game-- the ESP Game You go and you are linked up with another online player. A picture flashes onto the screen and you have to type in possible keywords to describe the picture. If you and the other player match, you get points and then move on to the next picture. People have been known to play for hours, the Journal reports.
Sounds like a good time-killer. But here's the catch: Von Ahn is using the game to label millions of unlabeled pictures on the internet. His theory is that humans do a much better job of this than computers, so why not get humans to do it.
Pretty darn brilliant, if you ask me.
PS: Von Ahn, who is all of 28, is also responsible for Captcha, that distorted code thing you have to correctly type before you can, say, post your comment on The Toad Stool.