It probably is not solved without a central authority that distributes and revoked identity tokens, like we have with passports. Decentralized proof of personhood is a pipe dream.
I'm not sure why this was marked dead (unless you're shadowbanned), but this is valid. I think the idea is for centralized entities to issue non-transferable tokens to accounts, which can then be used to verify that account's "personhood" as you call it, while preventing multiple accounts from getting one for the same person.