SNAGU, a project by ITP students (NYU):

snagu is a camera-phone based scavenger hunt with no limits on time, space, or answers. it was created by four students from nyu's itp, pollie barden, cory forsyth, jaki levy, and oren ross, and won the cisco/ mtvu digital incubator grant. it is currently being play-tested before the september national launch. (...) the game is basically a reverse of flickr, rather than tagging a photo, you photo a tag. we will send you your first tag right away, and you just send your photo to you receive the next tag only when you send in your picture or pass on the tag, you control the pace. then you can then go online and vote for your favorite picture. the more people that play, the more fun it becomes, so feel free to send this along to any friends!

They're still developing the game that will be launched in September in the US. They need help for playtesting.