In case you missed it, here is their step by step advice, however I skipped step 3 and it still worked:
1. Back up your iPhone to your PC using iTunes.
2. On your PC, download and install iFunBox, a free utility that will allow you to access the system files on your iDevice; (try www.i-funbox.com)
3. On your iPhone, go to Settings\General\Usage\Storage\Music and swipe and delete All Music. (probably not necessary)
4. Turn off your iPhone, then restart it.
5. Put your iPhone in Airplane mode so it will not be disturbed while syncing.
6. Make sure iTunes is not set to start automatically when a device is connected and close it on your PC if open.
7. Run iFunBox and connect your iPhone via cable to your PC. Look for the "iFunBox Classic" tab and click on it.
8. Connect your iPhone via cable to your PC.
9. Your device will appear under "Connected Devices" in iFunBox.
10. Navigate to the file, "MediaLibrary.sqlitedb" in folder "Raw File System>iTunes_Control>iTunes."
11. Rename, "MediaLibrary.sqlitedb" to, "MediaLibrary.sqlitedb.backup." (Note: Do not rename or delete, "MediaLibrary.sqlitedb-shm" or, "MediaLibrary.sqlitedb-wal." Neither of these are the file you're after!)
12. When done, eject / dismount your iDevice from iFunBox, then disconnect the cable.
13. Close iFunBox. Reboot your device again by turning power off and back on. (Again, may not be necessary, but it wouldn't hurt.)
14. Start iTunes on your PC and reconnect your device to the sync cable.
15. Sync your device. When done, be sure to eject / dismount your iPhone from iTunes before disconnecting the cable.
16. Take your phone out of Airplane mode.
17. Check to see that your album artwork has returned.