The short answer is that fanpop provides an "image credit" field which every user should use to make it clear that no ownership o rights to the imágenes are implied por being publicado here: the imágenes still belong to <these people> (what tu insert in the image credit field).
Do a buscar of fanpop (or just participate in a foros long enough) and tu will quickly find dozens of pages of people discussing how to properly use the image credit field. One fairly straightforward method is described in this article:
link
