This script will embed artwork that has already been downloaded (via the iTunes "Get Album Artwork" command) into the files of the selected tracks.
Also see Re-Embed Artwork.
NOTE: For best results, use with an album's worth of tracks--or so--at a time. iTunes may be obliged to perform a number of background tasks when applying image data and may prevent the script from proceeding if a large amount of data is involved.
Note: (August 2014) Not sure what the issue is but results are inconsistent with modern versions of iTunes.
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Create two playlists containing tracks with JPEG and PNG artwork
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Swap the name with the artist of selected tracks
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Apply selected CD's CD Text to its disc and track tags
downloaded 14m 55s ago
Correct song titles listed as "Artist - Song Name"
downloaded 51m 38s ago
Gather audio tracks whose files contain no artwork metadata
downloaded 53m 13s ago
Restore each selected track's artwork from an image file stored in its Album folder