I have recently subscribed to iTunes Match on the cloud and noticed some album artwork was not showing up on my iPad. I read several posts from people having the same issue. After kicking this around I found a fix that has worked every time for me and may help you as well.
Overview: The art was on my iTunes library, but some art did not make it to the iCloud and was not showing on my iPad - "Albums" Section of iTunes while streaming.
1). Identify an album that is missing the art from your mobile device.
2). Go to that album and select the first song from iTunes (All Songs) on your computer.
3). With the song selected do a "Command i" to expose GET INFO for that particular song. There are several tabs at teh top of this GET INFO window... the last one is ARTWORK.
4). Click on the art then drag a copy to your desktop.
5). Go back to the GET INFO and highlight the artwork once again and click DELETE ...then OK.
6). Poof, the artwork will be deleted from the GET INFO and will no longer show for that song.
7). Go back to GET INFO window. (command i) ... click ADD in the ARTWORK tab.
8). Select the art file from your desktop (or where ever you dragged / saved the original to), click OK. I used a few personal pictures for some art and it worked too!
I did several this way and once I was done I did an UPDATE iTUNES MATCH from iTunes (found on the STORE Tab...not the store itself). I closed iTunes on my iPad and re-opened it...presto, the art work came in.
My ARTIST tab still has a few missing covers but it is coming!
Hope this works for you!