[read_if_gay_]

Steganography is cooler for sure, but can't PNGs already store arbitrary data in the header? IIRC, the game Spore did that so you can exchange creatures by sending images.

[nacs]

I think the issue with that is that many image hosting sites optimize their images or at the least strip unnecessary data and EXIFs.

So at any point while being copied from person to person, that game data could be lost.