Earlier quoted context omitted.
yes and no. It's easy if you just want to display your own content: https://www.invisible-computers.com/invisible-calendar/image... or, if you want to share your app with others, there is: https://github.com/Invisible-Computers/image-gallery/blob/ma... It's hard if you want to run your own embedded code. I just haven't written the documentation for it and you would need your own UART flasher board.
Wow, very clever, just display an image! Does the image server really have to be on the Internet? Can I just enter a locally-resolvable hostname or IP address?
I have some ideas for letting users point the device directly to a local URL, but I don't want to commit to any promises on that front.
You could try using something like https://ngrok.com, that's what I sometimes use for testing.