I think all your songs need cover art.
I WILL BE MAKING COVER ARTS. eventually. theres a thumbnail property on the artifact data which is percisely for this reason.
This is because some people could use them as a reference to design the levels in 'A Dance of Fire and Ice' and 'Rhythm Doctor'. Without these, the levels might be quite bland if the creators don't have any ideas for design.
Especially 'party with the gang of 3', because I'm MAKING that level. Could you make one album cover on the spot for it?