What an amazing image! It's an 1880 painting called "Cain flying before Jehovah's Curse," by Fernand Cormon. It's at the Musée d'Orsay (in Paris), so I guess I've seen it, but I don't remember it.
Despite his moment of glory as a Beaux-Arts professor..., [Cormon] was almost forgotten by 1924 when he was run over by a taxi outside his studio, and is barely remembered today save as the teacher of more illustrious pupils.Here's the relevant passage in the Bible, Genesis 4:16: "And Cain went out from the presence of the LORD, and dwelt in the land of Nod, on the east of Eden." I don't know where he got all those other people going with him or why they looks like cave-folk. I'm guessing Cormon was stoking our doubts — making it look especially bizarre to make us think about how bizarre the Biblical account really is.