To change the artist's image Get Info on the image in Artists then select the "Artwork" tab and insert whatever image you want for the Artist. NOTE: You can change the artwork associated with album in the same manner by selecting the album instead of the artist.
Thanks.
I wasn't explicit there: The artists are part of my library; it's those obnoxious images that I want to get rid of.
Nope, that doesn't work; the Get Info you've suggested doesn't affect the artist's image...neither shows the current one nor offers a "Reset Default" option, and specifically refers to album artwork.
I wonder if those images are stored in one of the databases in Music Library.musiclibrary?