Per the FAQ:
Can" class="bold plain" rel="nofollow">http://www.rubberslug.com/resource/faq.aspx#3-7
"
Can I post artbook scans, manga scans, postcards, etc.?
No. Objects that are not original studio-produced originals are expressly forbidden on the site. This is the one really big rule here. Rubberslug doesn't make enough money to handle a lawsuit from a copyright holder who "just doesn't get it". You can provide all the disclaimers you want, but at the end of the day, it's ALL sites that will get shuttered, not just yours."
but see also:
http://www.rubberslug.com/resource/faq.aspx#4-1
"May I use copyrighted graphics in my banners and site graphics? Like from a video game?
Here's how it works: technically, you're not allowed to have copyrighted art on your site. If you're using one or two illustrations in a banner graphic on a non-commercial site, it's unlikely you'll get in trouble. If you post a scanned collection of every artbook you own, it's far more likely you'll get in trouble. (And not only from us.) "
I've got (as banners) some non-cel artwork and I think that is OK per the second FAQ question even though it violates the first question. Meybe clarification from a mod would help?
Either way, if someone has a gallery of artbook pages (or probably even covers) I'd say thats way not allowed, but I don't make or enforce the rules :)