Chris Lilley--one of the original PNG co-authors--has a post with an example HDR image: https://svgees.us/blog/cICP.html It is about half way down, with the birthday cake. Generally, us tech nerds have phones that are capable of displaying it well. So perhaps view the page on your phone.
What you should look for is the cake, the pink tips in her hair, and the background being more vivid. For me, the pink in the cake was the big give-away.
There is also the Web Platform Tests (WPT) which we use to validate browser support: https://wpt.fyi/results/png/cicp-chunk.html?label=master&lab...
Although, that image is just a boring teal. See it live in your browser here: https://wpt.live/png/cicp-chunk.html
For an example of APNG, you can use Wikipedia's images: https://en.wikipedia.org/wiki/APNG
But you have a bigger point: I should have live demonstrations of those things to help people understand.