I restored my iPhone 5 from an iOS 7.0.6 jailbreak to iOS 7.1. I restored to a backup. During the syncing of songs from the backup to my iPhone it accidentally got unplugged. I plugged it back in and synced my songs manually (not from the backup).
Now 5 songs that I bought from iTunes have all lost their album cover on my iPhone. All the other album covers from other songs are still there. It's not a big deal, but I like to have all album covers filled in.
While I was typing this I remembered that it helped to completely delete the album covers and download them again, I did this, now only 2 albums are naked, so to speak.
Best Answer
I had this problem and through asking google I figured out a solution. Your best bet (it worked for me) is to go to your iTunes, sync your iPhone and then go to music. Once you are at the music tab, you want to uncheck the "Sync Music" at the top (this will get rid of all of the music without album covers, it will be okay I promise). Then you want to sync your phone so it gets rid of the music. Then once that is completed, you want to recheck the "Sync Music" and sync your phone so it reverts what you just did. It will take a few minutes for the music to get back on your phone so be patient! Afterwards, everything should be peachy keen :)
Hope I could help.