There is a calendar being sold with great blues art from both ads and 78 picture sleeves. Some of this art also appears in books like "Early Downhome Blues." So beautiful pictures did exist on some sleeves, but they weren't the norm.

If you have a few bucks to spend, I highly recommend the Bear Family CD Box set of all the Carter family's original sides. It comes with a book filled with photos and other illustrations which you could scan and reproduce for your wall.