When you say "non-profit" I assume you're speaking of people who aren't profitting from their artwork, rather than a legitimate section 501(c) non-profit organizations, yes?
Whether or not an infringement has taken place has nothing to do with whether or not any money has changed hands. If someone uses copyrighted material without permission of the copyright owner, and either distributes their derivative work (which a montage of altered screenshots or graphics is), or displays it publicly, it's an infringement.
However, if it's original artwork that a fan has drawn or painted, they could certainly exhibit it publicly, and even sell it. But taking screenshots or photographs and making a montage is different.
Hope this helps,
Aisling