OS X 10.8 or later only. This script will export the artwork of the selected tracks (or the tracks in a selected playlist) as an image file to the folder which contains each selected track's file--presumably the track's Album folder--or a single user-selected folder. If multiple album tracks are selected, the script will make sure only one artwork file per Album is exported.
Also see Save Album Art as folder.jpg.
This Preferences pane for the script remembers your settings between uses.
Convert or import tracks with any encoder on the fly
Drag-and-drop to convert audio files with iTunes
Displays files in iTunes Media folder not in iTunes track library
Batch merge and/or delete playlists
Delete characters from the beginning or ending of selected tracks' name, artist, album, comments, composer, or show tags
Fill a playlist with user-set number of randomly selected full albums