Image tagging multiple music files

[Paul Johnson <baloo@ursamundi.org>]

I have a directory of music full of subdirectories sorted by artist,
and inside the artist directories, by album.  In the album
directories, there is one or more tracks, and a cover.jpg file with
the cover art.

My iRiver E100 is able to display this cover art, if it's part of
the music tag.  easytag can add this cover art to the track, but
only interactively, which is certainly tedious when you have a
nontrivial number of albums to tag with this art.

What is the easiest noninteractive method of adding the appropriate
cover.jpg to each track across multiple directories?