How do you ensure it includes every human?
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_.
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.
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