If you are using iTunes and CasaTunes is showing the same cover artwork for all your songs, but iTunes shows cover art normally, there is a good chance that your music is not organized into separate folders per album. You can fix this easily by:
1) Open iTunes. Open the “Edit” menu and select “Preferences”. Click on the “Advanced” tab and check the “Keep iTunes Media folder organized” checkbox. Click on OK
2.) Open the “File” menu, click on “Library” and click on “Organize Library….”. Check the “Consolidate files” checkbox and click OK.
3.) Run CasaTunesSync and synchronize. Exit when done.
4.) Open the CasaTunes user interface, go to Select Music and click on the Refresh Library button.
The Album Cover Artwork should now match the way it looks in iTunes.

By changing the Preferences to Keep iTunes Media folder organized, when you add music to iTunes, iTunes will create new folders for albums and artists and CasaTunes will show the correct Cover Art.