mind if I ask what it will be for? it looks nice
http://chevereto.com/ but I do not see how phpbb3 needs it (apart from the no database) . I don't understand what it is the mod will do basically.
the phpbb3 gallery mod is ok for most internal image hosting and then there is
http://coppermine-gallery.net/ which has a very good phpbb3 bridge that allows your users to have their own galleries. It has lots it's own plugins and stuff. for just a free image hosting service, there are already so many good ones.
I have personally used the phpbb3 / coppermine 1.5 combo. it is actually really good and bridging is easy. both are solid platforms that are very good at what they do.