If the artwork is not in iTunes on the computer then:

Add artwork to songs and other items

Music and video you buy from the iTunes Store comes with artwork. You can add your own artwork to songs and other items in your library.

You can add many types of still image files, including JPEG, PNG, GIF, TIFF, and Photoshop. You must convert WAV files to another format before you can add artwork to them.

Add artwork to music and video

Do any of the following:

• Add artwork to one item at a time:
  1. Select an item in your iTunes library and choose File > Get Info.
  2. Click Artwork and do one of the following:
     • Click Add Artwork, select an image file, and click Open.
     • Drag the art file to the artwork area.

• Add the same artwork to multiple items: Select the items, choose File > Get Info, click Info, and drag an image file to the Artwork area.

• Retrieve album artwork from the iTunes Store for songs in your library: Control-click the songs and choose Get Album Artwork.

If the artwork is OK in iTunes on the computer

First

http://www.mcelhearn.com/deleting-the-itunes-album-artwork-cache-folder-may-reso lve-problems-with-album-art-displaying/

Next:

- Reset the iOS device. Nothing will be lost      

Reset iOS device: Hold down the On/Off button and the Home button at the same time for at

least ten seconds, until the Apple logo appears.

- Unsync/delete all music and resync

To delete all music go to Settings>General>Usage>Storage>Manage Storage>Music>Tap edit in upper right and then tap the minus sign by All Music

- Reset all settings                            

Go to Settings > General > Reset and tap Reset All Settings.

All your preferences and settings are reset. Information (such as contacts and calendars) and media (such as songs and videos) aren’t affected.

- Restore from backup. See:                                               

iOS: Back up and restore your iOS device with iCloud or iTunes      

- Restore to factory settings/new iOS device.                       

If the artwork is in iTunes and on the computer but does not sync to the iPod then rest, you have to go through the actions in the last part of my previous posts. You do the actions one at a time and stop when the artwork syncs