I like it
Hosting would be the first issue to tackle. There are a ton of options, so shouldn't be an problem though. There would have to be some sort of filter in place to keep people from abusing it. There would need to be a way of efficiently indexing the photos as well. Users could submit keywords, but if not done properly, it could turn into a cluttered mess. Manual intervention would work, but could be tedious. I guess a manual filter would maybe be needed anyway though, for quality control purposes. That all doesn't necessarily have to be beforehand though...could use a feedback system.