How do you ensure it doesn’t include every non-human?
I’m not even asking about computation or algorithms. I straight up don’t think you can make a definition that isn’t a tautology or an approximation. Both of which are useful, but neither of which can fit a _proof_.
You're not wrong, but something can work well enough to still be useful despite falling short of the idea of a proof or any formal definition.
Let's say that 95% of individual humans can pass it and only 2% of bots. For someone maintaining a website, who has to decide between using this system and shutting down their site because of the increased costs, that may very well be good enough
That’s a pragmatic and understandable argument. And for an individual hobbyist site owner, that’s fine. Are we okay with excluding 1 person in 20 from the services of a midsized organization? What if they’re integral to the workplace? Or a major transport provider without differentiated competitors? What if the organization is a state government?
Every place on earth has some legal definition of who is human. The system I’m thinking of isn’t a technical/captcha one, it’s a human curated list of humans. Just an electronic ID. Those already exist but the challenge is making them (acceptably) privacy-preserving.
I want to take my existing national digital ID and use it online basically. BUT I don’t want the websites to know it’s me. Just that I’m human (or perhaps over a certain age). And I don’t want the ID issuer to know what site/service asked whether I’m a human or I’m 18 etc.
We’re talking about privacy-preserving proof of age, but as we see here the real utility of such a system will be proof of humanity.