Specifically with PNG it has a concept of "private" chunks which you can use to store arbitrary data. Conforming decoders will ignore these chunks, and may or m

Specifically with PNG it has a concept of "private" chunks which you can use to store arbitrary data. Conforming decoders will ignore these chunks, and may or may not drop them if the file is modified. See https://en.wikipedia.org/wiki/Portable_Network_Graphics#%22Chunks%22_within_the_file https://en.wikipedia.org/wiki/Portable_Network_Graphics#%22C...