The rest here is a collective noun, though I will not argue with the English if they say it sounds weird (even if you treat "the rest" as one "flock").
Well I'd use what you're reffering to as reference to be honest. If you'd written "The rest of the pictures are ..." it would have been a perfectly normal sentence. Since you're using "the rest" as a reference to "the pictures" I'd use are. I'm no expert though but I tend to simplify sentences a bit for them to at least resemble something correct.
PS: Not that I'm suggesting your sentence isn't resembling of something correct or anything like that.
Aaron
