Update: Oh, well, I finally just trashed everything, one at a time, and found that those images somehow lived in Library.musicdb. They're now gone, and I've got to reconfigure my Music window...GIANT PIA!
Huh, so you couldn't take my guess about it 🙎ðŸ»â€â™‚ï¸(that emoji is a "man pouting") 😊
You didn't guess about anything; you confirmed in Ira's thread that the problem lived somewhere in Music Library.musiclibrary, but not precisely where, so I took a quick first look, threw in the towel, and then decided to go for broke.
FWIW I just checked and verified the Music folder is included in Time Machine backups so it is recoverable and you wouldn't necessarily need to reconfigure your Music window.
To which Music folder are you referring?
I backed up the contents of Music Library.musiclibrary before trashing them, but the only way I could get rid of the images was by trashing whatever contained the window settings. (Restoring them wasn't as big a PIA as I imagined it would be, but going back to reset things that were set, literally, YEARS ago is always a daunting task.)
