Yes, It is a nice idea. Having a team of some / 10 active users must.
May be they can initiate the Photo themes for which other users will post their creativity.
But there should be condition to upload images shot by camera or mobile and not copy paste from net. Every month winner will be chosen on the quality of photos upload.
Thats a good idea.It should be properly moderated, with some limit on daily upload of photos, some helpful criticism on the photos uploaded so that the members can improve their techniques, information on editing techniques etc., could be thought of.