I've been experimenting with loading photos not taken on the toy camera and loading them onto the camera just to print them out... I think you need to get a small file size and maybe(?) remove metadata... though it may also be an issue around how some software writes a JPG.
I don't know if anyone else has figured this out yet, but if not, I'm working on it through trial and error.
@pwalck@erik@concretedog@ge0rg@tobbsn Hey, guess what? I may have been overthinking things... Today's test was, take a photo on my phone, open in Preview.app, export JPG at around 700k, copy to SD card and then... print!
I loaded a thermal shipping label in the toy camera (after cutting it down to size) and it printed just fine. Thermal is thermal I guess. I should probably find more rolls of thermal paper as well.