I used FixTunes (google it). $24 - pretty decent - it assisted in fixing about 75% of my collection, but I don't know if there is a magical product that can fix 100% (if anyone knows, please let me know too). FixTunes also takes a long time after you have identified to run a fix. I have tried microsofts free tool "Album Art Fixer", but that tries to fix "Album Artists" which 99% of all music DOES NOT contain; however it does let you add custom album art, but with a large collection, it would take years to complete.