You'd also want "seed" and "engine" attributes to ensure all visitors see the same result.
Not so much for us on earth however.
One of the best uses of responsive design I've ever seen was a site that looked completely different at different breakpoints - different theme, font, images, and content. It's was beautiful, and creative, and fun. Lots of users saw different things and had no idea other versions were there.
That idea is something that is only cool in theory.
Currently, we're definitely not there in terms of space/time tradeoffs for images, but I could imagine at least parameterized ML-based upscaling (i.e. ship a low-resolution image and possibly a textual description, have a local model upscale it to display resolution) at some point.
It’s utterly impractical, but fun to muse about how neat it would be if it weren’t.
By comparison, you could easily define a number that goes 0,123456789101112131415… and use indexes to that number. However the index would probably be larger than what you're trying to encode.
I am curious what the compression ratios would be. I suspect the opposite, but the numbers are at a scale where my mind falters so I wouldn’t say that with any confidence. Just 64 bits can get you roughly 10^20 digits into the number, and the “reach” grows exponentially with bits. I would expect that the smaller the file, the more common its sequence is.
Let's do it for a similar number but in binary format… a 1mb file has 2²⁰ digits. If we optimize the indexing to point to the "number" instead of the "digit"… so that the index is smaller. Magically the index is as long as the file!