iTunes Default Album Artwork

"If I do what you suggest, it will not allow artwork of any kind to be assigned until I put it there, correct?"

Yes, as far as I know, that is correct. Just remember to deselect "Automatically Update Artwork for Imported Songs"

Select the song/s or album/s then, ⌘I to get info. Select the Artwork tab, click on the image and ⌘Delete. Click ok and the artwork will be gone. In the preferences menu under advanced deselect "Automatically Update Artwork for Imported Songs", this will prevent Music for downloading artwork.