Ironically jpegoptim is pretty happy to knock img1.jpg (woman eating donut) down from its original 55kB to 33kB with no perceptible-to-me quality loss though ;)

It is a lot smaller than that, that is probably the size of all JS code on the web page?

The algorithm itself fits into a few k.

Yeah, you're right. I found the first JS file in my network tab and judged by its blurhash.js filename that it was the algorithm: https://blurha.sh/blurhash.01ae00eea611ada5e9c7.js

Of course, my first clue should have been that it was also the only Javascript file.