My guess is by using ID verification similar to how I do it on https://onlyhumanhub.com/
I'm curious about how this works, but it doesn't look like I can find out without creating an account. I see that it says "Link your existing social accounts to prove you're not a bot." How does having social media accounts prove I'm not a bot?
So you have just built a wrapper around https://passportreader.app/, which itself is reading NFC enabled ID/passports from specific countries. The coverage map is here: https://passportreader.app/coverage.
Might be good to know that even in the US this approach would only work for ~50% of people, since a lot of people don't have passports. In most countries this does not work at all, since they don't issue NFC enabled ID/passports.