it is amazing to read what is possible with the JPG format:
My recollection was that this was called Progressive JPEG, as in, it would show progress as it loaded. In practicality, I only remember seeing it used for animation once or twice because animated GIFs were not far behind.
I remember the experience being an image getting more and more clear as it downloads, in the way of the “Enhance!” behavior from NCIS.
.jpg was under license then (probably).