Is there are place to report missing/incorrect album art to the iTunes team?
you can always use Apple Feedback page to submit any kind of request.

if you have this problem in our own iTunes Library, it is easy to assign a new cover to the song or album by just dragging the cover to it or using the GetInfo option, you know how to do this right?

if you install Last.fm app you can simple play a song and then drag the last.fm cover into the artwork of the iTunes song.