Proof of Personhood

There are three main families. Biometric or hardware-based, such as World ID, formerly Worldcoin, whose Orb device captures iris and face, confirms humanness and uniqueness, turns the iris into a code and splits it into shares using multi-party computation (MPC), deleting the images on-device by default. Social graph, such as BrightID, which builds a network of connections and runs a sybil-resistance algorithm without biometrics. And credential aggregation, such as Human Passport, which combines stamps from several providers into a score.

It is the bottleneck that keeps on-chain reputation and governance from being gamed by buying wallets. It serves to distribute airdrops without abuse, to support quadratic funding like Gitcoin Grants, to enable one-person-one-vote schemes and, increasingly, to tell humans apart from AI agents. Without a human-uniqueness layer, any merit-based system can be inflated with duplicate identities.

It is not the same as a DID or a verifiable credential. Proof of personhood attests human uniqueness, while a VC proves a specific attribute. In fact, a single proof of humanity can be issued as a verifiable credential or as a Soulbound Token. It is therefore a prerequisite for sybil-resistant on-chain reputation and honest on-chain identity. Other examples include Proof of Humanity.