From the Copyright for Collage Artists web site (http://funnystrange.com/copyright/derivative.htm): "Most important to the collage artist is that a derivative work can only include copyrighted material if it is created by the owner of the copyright on the original material, or with that person's permission. This means that making a collage that includes photos from National Geographic, Rand McNally maps, or pictures of Andy Warhol paintings, is illegal unless you have obtained permission from whoever owns the copyright on those works."