Thanks again, William.
To clarify the situation, let's make a small (realistic) example:
I sell a (social) site to a small city (let's say 5.000 people): there will be people writing articles about the local sport teams, music groups, events, classical concerts, political problems, and so on...
Each one will want to post some picture, and I see as a plus that people, that are always curious! :-), can browse ALL the picture inserted in the site, ordered by reverse date, or ALL the picture in a category (sport, music...)
I think it's strange that noone thought about a little service like this, it shouldn't be difficult, and would be a great service!
Think also to have a little module on the home page with the last 5 pictures inserted by users... it would surely make people come back often just to see if they know someone, if there is something funny...
Andrea