This image goes back as far as 1960.
There is an ad for Luigi Franchi shotguns designed in 1960 by Aldo Calabresi which has a silhouette of a man shooting the exact shotgun as the Zbikowski "Willie Boy" poster. Zbikowski changed Calabresi's hunter's hat into a cowboy hat and slimmed up the man. The Ames Brothers redrew the hat and arm. Jeremy Wilson redrew the hat, added the cowboy's body and changed the double barrelled shotgun into a sort of single barrelled gun.
I have a jpg of all four images side by side I can email to anyone who wants to see them.
Zach is right, there are a lot of posters on this site that rip off Cieslewicz, Pagowski, and Jan Lenica. Not ripping on this poster per se, just using this thread to comment.
I think the internet makes it bardzo latwy to "borrow"...
I usually don't really care, but what really killed me is that they have a little signature in the corner, as if to imply that they drew it. Taking something and reworking it is one thing. But taking something, tracing it, signing it, and selling it as merch is...
I'm not saying it's totally original, but at least I changed and added shit to it, unlike the Ames Bros who just took the exact image and faded it a bit.
I'm less of a thief than they are. But hey, I admit it, still a thief.
The outline of the hat and shoulders are from a polish poster from the '70s. I changed the double-barreled shotgun to a single shot rifle, and added a torso and legs, as well as a few other things.
I think there's enough different to distinguish it from a complete ripoff. More an inspiration.