Check out Spogger, the latest Silicon Valley start-up focused on photo tagging.
On the good side:
..it’s possible to provide near real-time info on just about anything — from items for sale, to traffic conditions, to the daily lunch specials at the deli down the street. The other thing that is interesting about the service is that, while it does jump on that tagging bandwagon, it also steps away from it with a classification system that lets people propose and vote on the proper classification for images.
Down side includes spam and disagreement about classification, but also:
…what remains to be seen is how seriously people use imagery for information sharing. Snapshots, historically, are more about aesthetics than pure information sharing — and while the rise of cameraphones (which both make it easy to take photos anywhere and to share them) makes it easier to use photos for information gathering and sharing, it is still a mental and behavioral change, that not everyone will be willing to make.
Also, interesting piece by Kevin Ryan on “tagvertising” here.