Hi there!

Official screenshots would be okay, as long as you credit whomever you get the screenshots from, like we do in our "Credits and Rating" sidebar on the left of your screen. Since the artwork is official and for non-profit use, we're under the impression that it falls under the Fair Use Act.

The above rule you quoted is more for fanworks, where the creators may have not allowed their created works to be used. For example, I am a freelance artist and am commissioned to do many fanworks; my art is not available for use as icons and signatures, and while I've seen it on Google images and other such image-gathering sites, citing that you've taken it from there would not be the equivalent of me giving permission, even if you wound up modifying my artwork to create a derivative work.

I hope that makes sense! Let me know if you have any questions.