There was once an online tool to convert an image and turn it into a ROM you could flash on a flashcart like the InsanelyGadgets ones. Sadly, all I could find was this.

https://ruben.cougil.com/assets/gameboy/

That said; GB Studio has a feature that lets you do that and in raw code (GBDK), all you'd do is convert the image down to the proper resolution and color pallette (gb, gbc), draw the image and add an infinite loop. So totally doable =)

I don't have gbdk set up, otherwise I would've thrown together something real quick. But if you have access to a Linux shell, it should be trivial to install, find the neccessary format, and... create a ROM that displays your npub. xD