Thinking about Flickr jogged my memory to check up on Flickr's progenitor, Fotonotes.net. The Fotonotes site looks a tad dormant, but Greg Elin had been threatening to open source his implementation, the protocols, and APIs.
Turns out the action is over on Elin's weblog, where volunteers are being taken to have a crack at his open source Fotonotes release.
I'd love to raise my hand, but I know just enough to know I'm at my project engagement limit. Maybe, I'll try my hand in mid-October.