I'm uncertain how appropriate it is for this to be news related. If you're doing a story on Burma, I want you to be in Burma, not in San Francisco sipping a Latte, posting an ad such as "Myanmar: $100 for picture of demonstrating anti-government crowd". That just seems like a recipe for non-trustworthy information. You are asking for evidence (pictures) to fit your theory (the story you intend to write). That isn't how good science is done, and I would think it's not how good reporting would be done either. You even go so far as make the sources anonymous, which takes even more credibility away.
However... I do see merit in the idea of a geo based Mechanical Turk type job board, that's not news oriented. If I'm a web designer or an advertiser, and I want a picture of a can of Coca Cola in front of the Salt Hotel in Bolivia, than this seems perfect for that sort of thing. If I'm a movie writer, and I want to know how many drawers the card catalog in the west wing of the library of congress has, because I'm using it for a plot point, than your service would be perfect. I just don't like it for news.