OS X 10.8 and later. This script will export then re-import the artwork data of the selected tracks.
Note: This script may not be able to handle processing more than about an album's worth of tracks per launch due to the way iTunes manages graphics data.
Also Note: (August 2014) Not sure what the issue is but results may be inconsistent with modern versions of iTunes.
Displays files in iTunes Media folder not in iTunes track library
Edit a selection of iTunes tracks' tags "old-school"
Remove iTunes tracks disassociated from files
Add or subtract a user-entered number from each selected track's Plays
Export artwork of selected tracks to parent or specified folder
Set choice of various number tags of selected tracks incrementally