I was surprised I hadn't heard of this, or his related project JPEG-Clear. I have thought for years that the JPEG-Clear method is how responsive images should have been handled in a browser. A single-file format that can be progressively downloaded only up to the resolution it is being displayed at. If you zoom in, the rest of the data can be downloaded for more detail. Doesn't require complex multi-file image authoring steps, keeps simple <img src> grammar, and is more efficient than downloading multiple completely separate images.
Loading a more detailed version of an image as you zoom in is different from what a progressive JPEG does.
Loading a Progressive JPEG means you still unconditionally load the entire file, you just are able to show a low detail version before it is fully loaded. The last time I saw a progressive JPEG actually take time to load was when I had dialup.
1. You can terminate the loading process as soon as you're satisfied with the quality. It's just that browser don't do that.
2. The OPs JPEG-Clear proposal [1] also loads the entire file no matter what. It's literally just a reinvention of progressive JPEGs, presenting it as something novel.
