More than a game, for Google this is a way to tag images using human brain power… to improve their image search results. Two people finding the same tag can serve as validation the tag makes sense. I suppose for Google it’s not important that two people find the same keywords at the same time – they can simply let people tag the images and then add any threshold they want (like “4 people must have chosen this tag for it to become a confirmed tag”).
Both Search Engine Watch and TechCrunch made the connection to research conducted by Luis von Ahn at my alma matter that was first blogged about as early as December last year (written up in the Pittsbrugh Post Gazette in August 2005).
Yes, Image Labeler is based on my ESP Game, which Google licensed. I’m not employed by Google, however, since I’m a full-time faculty member at Carnegie Mellon.
Interestingly, Riya uses a similar but closed system of human tagging to populate its object search. It’s unclear how such a system scales for web wide results unless something like Google or Amazon’s tool find enough widespread pick-up and open up an API to the tagged images.