Nothing's going to work for every band though, Loop (80s indie band), give rubbish results in all 3 scenarios. (Loop band gives pictures of some wierd excercise device)
"Loop music band" returns better results. But I'm not sure it will do good or harm for other bands. Probably it will depend.
BTW in case you're not aware, the patch file gets constantly updated and all the things discussed here were already implemented to the latest 3.3 patch.
I did some more tests. For big name artists, any conditions work, so they are not a problem.
For obscure artists and classical music artists, current restriction of "large" and "wide" certainly drops a lot of good artist pictures for them.
You might want to try with "larger than 800x600" with no aspect ratio restriction.
Also dropping either "Music" or "Musician" from the search terms for a person-type artist seems working better. The exception is some cases where the artist name is also used by other celebrities.