Sorry if it wasn't that clear, I know it's a bit complicated. To put it simply... you can design a "cover" or "poster" for the fandom, pretending someone is making a book, movie, or a musical based on it. You can also use photoshop to mimic an already-made cover/poster, and spoof off of that. (Or just draw the cover/poster that's based on the other one.)

Okay, let me give you an example: Say you wanted to do a movie poster. You could either design your own, or photoshop it so it's one of the HP movie posters, but with faces of people in the fandom. OR you could draw such a poster.

Does that make a little more sense?