Sorry I didn't reply straight away, I wanted to give it some thought before answering and unfortunately I've been working late today.
Howard is right that there could be storage space and bandwidth issues with providing a service like you suggest, especially if individuals were to be able to post their own photos, like they can on Flickr for example, and it would depend on finding a suitable package that would allow sufficient control of those aspects.
There are some great photos on the Marple Flickr Group and maybe the best way would be to join in that as it is already established. It would be nice to link into it from the site somehow though.
An alternative might be to use the Virtual Tour, as we do nowadays for current events. The only problem with that is that the photos would have to be submitted by email rather than unloaded by the photographer.
I will think on it some more for a while and see if any useful ideas develop. In the meantime I would be keen to learn anyone else's thoughts on it. How many people would be interested in contributing if it were possible to set something up? Perhaps there is not sufficient interest?