Currently the MusicBrainz guidelines do not allow pseudo-releases to have artwork uploaded on them.

Thus, the only proper way to fetch the correct artwork would be to take them from the official release instead.

We already have relationships to point to the right release. It's just that a redirection is necessary.

Alternate MusicBrainz tracklists MBS-4501 would also fix this issue, of course, because there'd only be one release and the artwork would always be correct.