iTunes: album art invites not - so go ahead
- Start iTunes and open the "settings". Press in and hold at the same time the keys [Ctrl] + [,] is pressed.
- You can switch to the tab "Store" and activate the Option "automatic loading Cover pictures".
- Then click the "OK" Button, tried iTunes to download the missing Cover art. The songs are matched with the information from the iTunes Store.
- Note: Should have some of the songs even after a restart of iTunes, no Cover, open it with a right click on the Song, the "information". Go to the tab "Info" and check the information for accuracy. Just a little tip-error here, can't download iTunes the Cover.

iTunes Cover download
Should this not work, you must use the iTunes-Cover to manually insert.