Now we need some tooling where you put in a maximum error bound, and it automatically finds the lowest resolution you can get away with. I wonder if one of those video-codec-based image formats (WebP, HEIC, AVIF) would already do something pretty similar if you just set a quality factor?

It seems obvious in insight but I never used this before. An interesting front end trick, though adding gradient backgrounds is something I avoid as it's mostly eye candy

Where's the hacking? It's common knowledge that if you stretch a small image, it blurs. As far as I'm aware, this is commonly used for backgrounds.