ArtDeCodex

ArtDeCodex allows you to decode iTunes 7 .itc files into plain old .png or .jpg files so you can use them outside of iTunes.
Prior to iTunes 7 and coverflow, these artwork files were stored as id3 data.

Since coverflow was introduced in iTunes 7, Apple has adopted the opaque and largely unreadable .itc format for files in the ~/Music/iTunes/AlbumArtwork folder.
With ArtDeCodex, you can easily translate these files to regular png or jpg files and save them where you choose.