A community may want to know that ten accounts represent ten different humans without needing to know the ten humans’ legal names.
Those are separate problems.
Identity verification asks who someone is. Proof of personhood can ask a narrower question: is this participant a distinct human who has not already registered another account in the same system?
That distinction matters for communities that value pseudonymity. A whistleblower, political dissident, abuse survivor, niche-community participant, or simply private person may have good reasons not to attach a government name to every public conversation.
There are several ways to prove uniqueness
Different systems solve the problem differently.
Some rely on government documents or phone numbers. Others use biometrics, in-person ceremonies, social graphs, trusted introductions, or networks of people vouching that other participants are unique humans.
The World proof-of-personhood whitepaper explicitly describes personhood verification as a spectrum of credentials with different accuracy and privacy properties. Its own approach includes biometric uniqueness verification, while lower-assurance credentials such as phone-number verification prove something weaker.
BrightID takes a different route, using social relationships and network analysis to resist people creating many identities. A 2020 review of proof-of-personhood systems examined BrightID and other subjective approaches based on vouching and social trust, while also pointing out weaknesses involving privacy, centralization, and uncertain resistance to attacks. See “Who Watches the Watchmen?”.
None of these methods proves everything.
Proving one human is not the same as proving a biography
A system might establish that an account corresponds to one unique participant while learning almost nothing else about that person.
That can be desirable.
If the goal is preventing one user from creating 500 votes, the community may not need a name, address, employer, birth date, or photograph. It needs a credible way to make creating the 499 extra identities difficult.
But uniqueness does not prove honesty. A verified human can still lie, coordinate with others, operate scripts, spread spam, or use AI to write every post.
Likewise, legal identity does not prove that one person controls only one account.
Every verification system moves the risk around
Biometrics can improve uniqueness while creating privacy and exclusion concerns. Government-ID systems depend on official documents and trusted issuers. Social-graph systems can preserve pseudonymity but may disadvantage newcomers or isolated users. In-person ceremonies are difficult to scale. Phone numbers are widely available but can be bought in multiples.
There is no magical “human” checkbox.
For Dead Internet Theory, that is worth remembering whenever somebody proposes mandatory real names as the solution to synthetic populations.
A network can seek evidence that a participant is human without turning every forum into an airport-security desk.
The harder design question is deciding what the community actually needs to prove, and collecting no more identity than that purpose requires.