There is this freeware program called "The Godfather". It can remove, copy or 'copy and remove' album art from mp3's on the harddisk of your computer to a folder of your choosing. I think it's just what you need.
Don't let the interface scare you off, it's overwhelming at first.
It's really just a matter of organizing your mp3's right, make sure they all contain album and artist tags, and then with a few mouse clicks you're on your way.