Note from 30 April 2022
When you start using an image CDN on a site with oversized JPEGs, without any change to the HTML:

Imagine when there will be accurate srcset/sizes attributes, better formats, etc. 🤯
When you start using an image CDN on a site with oversized JPEGs, without any change to the HTML:

Imagine when there will be accurate srcset/sizes attributes, better formats, etc. 🤯
JPEG XL isn't useless; it is genuinely compelling technology for use cases beyond the Web. I'm just not personally convinced we need it in browsers…
The present and potential future of progressive image rendering
So if the browser manages to download 6 kB then stalls, then AVIF can produce a better result. But since the AVIF rendering is only two-pass, if the…
kliksphilip
JPEG VS AVIF - The Battle of Compression
In this super thorough study I test one single HD image and come to vast sweeping conclusions about JPEG XL and AVIF. But that's still one image comparison…
Should I please Lighthouse with modern image formats, or my visitors with progressive rendering of large images in my photography site? 🤔

Of course, this would be much easier with genaralized JPEG XL support, both modern and allowing progressive… 🤷♂️
Most mentions of the magical CSS object-fit: cover; in development tutorials should be accompanied by a warning: in most situations, it means the browser will download an image that is larger than required (at least in one direction), and optimization on the server side could be a better option.