Right now, it's not clear from the release page where the cover art comes from. It's been pointed out by several people, but http://forums.musicbrainz.org/viewtopic.php?pid=21225 is what prompted me to finally enter the ticket.

I think a fairly simple and not too intrusive way to improve this would be to display "Cover art from Amazon" for covers from ASINs and "Cover art from www.example.com" for covers from cover art relationships (where "www.example.com" is the hostname of the image) under the image when the image does not come from the the CAA.

The page footer already says cover art comes from the CAA, so I don't think there's any need to add an extra notice for the CAA images.