I've done the following:
1) moved all my mp3s out of the /home/public/data/audio directory into a temporary directory.
2) cleared the pluto_media table as instructed in http://forum.linuxmce.org/index.php?topic=6408.0
3) deleted all .id3 files from the temporary directory
4) deleted all files contained in /home/mediapics and /home/coverartscan
5) using mediamonkey tagging software, removed all album art from all mp3s in the temporary directory
6) moved mp3s back into /home/public/data/audio
7) ran resynchronize media from the web admin
Here is a sample of the output: http://pastebin.com/f6ea4cc01
The album art returns. It seems to have stored http://ecx.images-amazon.com/images/I/411%2BhkH0hYL.jpg somewhere other than the locations I've been clearing. Can someone explain how to thoroughly cleanse my library, short of doing a reinstall? I'm out of ideas.