I know that this feature is gone in itunes 11. The problem is that I can't figure out how to work around that. I read that rating an entire album and all it's tracks as 5 star will set that to default but that doesn't work either (and I tried a restart). The only way I can figure it out is to first change the artist name to something else for which ever artwork you want....then change the rest of the artists names AFTER that to match the new (wrong) name. After that the artwork is set to whatever you picked and you can just change the name back to whatever the correct artist name is. Obviously that's a crappy workaround but there has to be some other, easier way of going about this.