There's an interesting little program that will draw images on a Linux framebuffer device. It's capable of a slideshow. Seems perfect for a Pi, except for the framebuffer part.
But I finally got it sorted anyway. The biggest hassle was that it wasn't happy with quoted filenames with spaces in them. Oh no, I had to escape the spaces. And `printf "%q" "some string"` doesn't escape the spaces, it just quotes the string.
But I now have a simple script to launch it, provided I find the right keyboard to be able to switch to a real console first. All those images I swiped from Chromecast and Windows 10 are coming in handy.
A bunch of technomancers in the fediverse. This arcology is for all who wash up upon it's digital shore.