The artist Funbun tells me that these were originally done by Gert Gagelmann aka Julie Delcourt. Funbun later modified them into spanking scenes, an example of this process can be seen below.
Can you guess which one is my favorite? ;-)
Smiles and Spanks, NaturallyGin.com
Smiles and Spanks 
Has to be the wooden spoon one, bottom right…!
Nope ;)
I’m going to guess it’s the one with the young man on the receiving end ; )
“This gallery is made up of erotic spanking and enema drawings and watercolours by Julie Delcourt (also known Richard Hegemann or ‘GERMAN’) modified later by member Funbun into spanking art.”
https://animeotk.com/gallery/showgallery.php/cat/941