Are you missing some album art from your media collection? What you need is the World’s Largest Cover Archive at CDCOVERS.CC
I’m not sure how accurate the “World’s Largest Cover Archive” statement can be attributed to be, but this could be your first stop for trying to finding the album art you’re looking for in your collection.
You can also join their site and help them increase their collection by adding covers from your own collection. Now if everyone could just do this without joining, I think that would launch them into being able to use the world’s largest tag with certainty.