Not OP, but PNG (and most image/video formats) allows metadata and most allows arbitrary fields. Good parsers know to ignore/safely skip over fields that they a

Not OP, but PNG (and most image/video formats) allows metadata and most allows arbitrary fields. Good parsers know to ignore/safely skip over fields that they are not familiar with. https://dev.exiv2.org/projects/exiv2/wiki/The_Metadata_in_PNG_files https://dev.exiv2.org/projects/exiv2/wiki/The_Metadata_in_PN... This is similar to HTTP request headers, if you're familiar with that. There are a set of standard headers (User-Agent, ETag etc) but nobody is stopping you from inventing x-tomtom and sending that along with HTTP request. And on the receiving end, you can parse and make use of it. Same thing with PNG here.