OS X 10.8 or later. This script will look for an image file in the parent folder of each selected track's file--presumably its Album folder in which you have previously placed an image file of some sort--and apply the data from that image file as artwork for the track.
Perhaps Also of Interest...
downloaded 18m 21s ago
Remove iTunes tracks disassociated from files
downloaded 26m 4s ago
Convert selected tracks and export the converted files to a new folder
downloaded 37m 7s ago
Delete characters from the beginning or ending of selected tracks' name, artist, album, comments, composer, or show tags
downloaded 39m 32s ago
Check scripts downloaded to your computer from dougscripts.com for latest version
downloaded 40m 6s ago
Gather audio tracks whose files contain no artwork metadata
downloaded 40m 17s ago
Resample selected tracks' artwork to user-set size limit