On a first try itunes Match got 95 per cent of my album cover art correctly.
Why? the vast majority of my stuff is not available in the itunes store and iTunes rarely can find the correct matching covers. My secret is Google and amazon and a specialty web site.
For the remaining 5 per cent, the suggestion here of creating playlist album art is missing a lowed me to pick up a couple. But flicking through my iphone in horizontal position allowed me to spot the rest.
I fixed the rest (all three or four of them) in iTunes 11.x by
1.)Selecting all tracks in album
2.)Right clicked get info and checked to see if uploaded artwork or was it now embedded.
3.)Right clicked Deleted downloaded artwork.
Was tempted to use find artwork but realized would then recheck every single piece of music in the library and might override covers. Did not use find artwork
4a.)If I couldn't find the artwork in my artwork folder,iitunes embedded it , I deleted it, and I have no original artwork) I went searching on line in Amazon, Google, or a specialty web site for my type of music and Uploaded covers
4b.)If could find the artwork c folder, Simply uploaded it it again
5.)Not sure what happened next but clicked on tiunes match and it seemed to ahve started from sratch.Dont reember turning it off. It went quite fast and much faster than first time
6.)Every other time I did above I simply did ituness update and all was well.
Limitations:
1.)I only had itunes match turned on in itunes and my iphone
2.)I did not have itunes active on any other computer
3.)I did not yet have iTunes active on my ipad
4.)Very fast wifi connection
5.)iphone was plugged into computer with itunes
My guess of the vast majority of problems with artwork disappearing again or wrong artwork reappearing is synching more than two devices any technology is quite complicated. I used to do two devices with outlook. The issue is any change to any copy makes that copy the newest copy and depending no how granular the synching is(version and date) vs (individual data fields),)the slightest change can bring back a copy that doesnt have all your changes. Network secruity with multiple devices is prone ot the same problem where on device notupdated fast enough causes lock out. If you want to see someone who did it right go to splash id before they used the icloud. They tagged every single item. My guess is apple is not doing that??