The first thing that occurred to me is that the Disney artists (or contractors) probably came across the image on Tumblr or Pinterest or some similar social image-sharing network, stripped entirely of its original attribution.
It's entirely plausible that someone would have thought it was a Disney-owned image originally, and in circulation in violation of copyright.
If that's true, it's not an excuse for using someone else's work without permission, but it would be a sad and ironic commentary on the sharing and re-mixing economy.
No, they won't.
Whether or not it was provided by a third party supplier is irrelevant.
It does not make disney any less infringing if they are the ones selling it.
It just means you can sue disney, and then disney can turn around and attempt to recover the damages you win from the next guy up the chain.
You absolutely, positively, do not need to sue the people all the way up the chain.
I am an IP lawyer (though this is not legal advice, just an explanation of general concepts :P)
If Disney is the one selling the bags, surely they are the only party it would make sense for the artist to make a claim against?
If I, A, lie to you, B, and as a result you take a supposedly-harmless action which is in fact a tort against aggrieved party C, I would expect you to be liable to C, and myself to be liable in turn to you. What did I do to C?
It's entirely plausible that someone would have thought it was a Disney-owned image originally, and in circulation in violation of copyright.
If that's true, it's not an excuse for using someone else's work without permission, but it would be a sad and ironic commentary on the sharing and re-mixing economy.