Totally unrelated, but I'm always reminded of Spore's (the videogame) save files. Creatures, buildings and such would be saved as .png and you'd get a nice preview screenshot of the creation, but the same file also contained the information for the game to actually load the thing. It was pretty cool
I don't think so, the images were pretty low res iirc. I did some googling though, and the only thing I found was somebody that said "the game reads the model data out from the file's alpha channel". However, I'd expect the data to just be appended to the end of the file, since PNG works anyway with that.
PNG is extensible, so they could totally have defined a PNG "chunk" in the private namespace and shoved the data in that. They didn't though. They treated PNG as just a way to store image data and wrote their extra data into the image, encrypted in an amateurish way.
even polyglot image/executables are usually _mostly_ two files mashed together. some cleverness is always required to construct a header that is valid for both formats, but then the trick is usually to make the executable jump past the image data (or, for interpreted languages, comment out the image data) and then store the executable payload at the end of the file.
