There are notable differences between this original painting and the printed cover — the science fiction elements have been added on the published version. Ziff-Davis often added such elements, changing one aspect or another of a painting in production in the printing stage, and most likely they added the wings to the horse, changed the hat to helmet with horns, etc., in the production stage.
This entire issue can be downloaded here
Beware the Wyvern witches!
Also, The Gods Fear Love