This is a great way to fix all your itunes album art.
its not reversible, so its not for the feint of heart.
1) open itunes
2) goto ‘albums’
3) press cmd+A
4) right click > get info
if it says ‘you are editing multiple items’ click ok
5) tick the box next to album art
this is about to set everything to have no album art…
6) click ok
7) it will edit all your music and set it to have no album art.
8) wait for ages while it applies
9)once its done and you have no album art, then go to albums again,
10) press cmd+A to select them all again
11) right click > get album art
12) wait till it downloads all the album art from the itunes store
13) run itunes match again to upload all the new data…