So Wildhoney, on yours, each time you add something to the pictures database, you get just the id, and then put the id in the pictures_category table, with the id of category? Then when you want to query them.. How exactly are you matching them? Maybe I need to read up on table joining. :)

EDIT: Ahh yes.. I've just read a few short articles. Join and Left Join looks pretty interesting, I may have to start putting it to use. :)