[pvorb]

Extending the format just because you can – and breaking backwards compatibility along the way – is even more pointless.

If you've created an extensible file format, but you never need to extend it, you've done everything right, I'd say.

[jajko]

What about an extensible format that would have as part of header an algorithm (in some recognized DSL) of how to decompress it (or any other step required for image manipulation)? I know its not so much about PNG but some future format.

That's what I would call really extensible, but then there may be no limits and hacking/viruses could have easily a field day.

[lelanthran]

> What about an extensible format that would have as part of header an algorithm (in some recognized DSL) of how to decompress it (or any other step required for image manipulation)?

Will sooner or later be used to implement RCEs. Even if you could do a restriction as is done for eBPF, that code still has to execute.

Best would be not to extend it.