I think https://discuss.atom.io/ could definately do with a proper “banner” topic that guides users at the rules of the site and teaches them a tiny bit about it, linking to main atom site and so on. Just don’t make it too big, only a few lines to give a “taste”.
I would place this extra rule in both TOS and FAQ. FAQ is the most natural spot as you get the badge “Read Guidelines” after reading it, we place extra importance to FAQ.
At the end of the day though you are going to have to be somewhat reactive here, update your FAQ and then next time it happens, flag the post and tell the user to read the FAQ, they should be correcting the images, not you, its too much work.
@purldator not sure why drive @lee-dohm off site to another unrelated area to discuss community building, this is a specific Discourse issue one of our paying customers is facing.