I wonder if those images are stored in one of the databases in Music Library.musiclibrary?
Almost certainly they are in one of the databases incorporated into the Music Library.musiclibrary package. I found the Belini image in Apple's Music library. I know that at one time Apple used a third party source for the album artwork and when there were multiple options simply selected the first one on the list. I haven't looked at every image in my artists list but as far as I can tell the artist image is either the entire album cover or a clip from the cover which is why I suggested changing the album cover.
