In order to share saved states of popular games around, it would be neat if you could put them inside a screenshot taken at this time, right? I first encountered this concept in a game called Spore. This is my own little spin on it, instead of storing the data in the header i'm reducing the colors a lot and adding the data on top.

https://github.com/mope1/image-store/

The data part is clearly visible on the left. This whole thing is not a very practical as most image uploady websites will re-encode everything to JPEG or whatever, but I found it kinda neat.