We could do usergroups also, with permissions, so the admin can put users into usergroups, and different usergroups are allowed to upload x amounts of images. Assigning moderators can edit other ppl comments, delete other ppl comments, delete other ppl images, etc.. w.e the admin desides that the moderator usergroup is allowed to do.

Also, when managing images, you should also be able to edit the description for it..