Multiple Album Arts for the same album?

I noticed a significant chunk of "other" data in my iPod touch 4g. I read on a mac rumors post about album art taking up a lot of this space.

After removing all of my music, I noticed that the "other" data was gone completely. Looking in the iPod's file system under var>mobile>media>iTunes_Control>iTunes>Artwork, I noticed that there are several copies of artwork for each song. I'd imagine this is what is eating up all that space.

Does anyone know why there are so many copies? And for that matter, if they are all needed and which can be removed?