Two things I don't quite understand:
Who is this user who is looking for a CD entry in the database, has seen the cover art, but doesn't have access to a spine?
Either they are looking for a CD they have, in which case they should have access to the spine.
Or they are tagging a legal download, in which case they should be looking for the digital release in MB, where we should use the cover art, or whatever the download service called it.
The other one is about the inconcistency of cover art.
Often a cover is completely blank - perhaps we should put our data in as [unknown] by [unknown] in that case?
Or should we use a consistent source of correct data that lets us tag our music accurately?
If we are going to base all of our data around people searching using a cover image perhaps we should integrate a google 'search by image' search or similar instead, which would be more accurate anyway. However my assumption is that those searches aren't that many, compared to, for instance, Picard tag lookups.
edit: Sorry I missed your other post - but honestly I don't think I need to give any more reasons