The actual hard problem about this proof of humanity is uniqueness. With CAPTCHAs you could just sit down and solve one CAPTCHA after another. You could verify account after account after account. You could be a Chinese click farm that does that, and then you could give these accounts to AIs. So something like CAPTCHAs doesn’t actually solve the problem at all. It’s a first-line defense against bots that cannot enter my website and watch my ads. CAPTCHAs as a whole won’t work for much longer because any reasonably smart AI is as good as you and me to spot the traffic lights.

Joanna Stern, I Am Not a Robot- My Year U…, loc. 1177