Google has created a fun way to help them tag/label all of their images within Google search.
Google Image Labeler partners you with another person online and you are given a time limit to match keywords for a given image that Google displays for you. Your point total is based on the amount of image tags/labels that you and your partner match This seems like an ingenious way for Google to provide more relevant search results.
Jason Law

Check out this google video on the subject from a while back: http://www.youtube.com/watch?v=dtFroEJN1nI
Google didn’t come up with this. That video really digs into the details and shows a some other examples where this is used.
And, is it just me, or is google’s execution of “the game” boring…
[...] This got me thinking more generally about the power of the “human computer” to accomplish other tasks, and I rediscovered Luis von Ahn, an Assistant Professor at Carnegie Mellon. He was obsessed with all the human computational time “wasted” playing Solitaire, etc., and suggested that image recognition and tagging could be done by humans if it was placed in the context of a competitive game. This was the inspiration for the ESP Game, later licensed by Google Image Labeler. [...]