Proof of personhood

How can a service confirm that a request comes from one real person, and not from many agents or many copies of one?

Once agents can fill in forms, write reviews, and hold conversations as well as people, the cheap signals that once stood for “a person cares about this” stop working. Options range from identity documents and in-person checks to cryptographic credentials, each with costs to privacy and to people who lack the right papers.

This bears on Friction collapse, on Citizenship and social membership, and on whether services meant for people, from benefits to voting, can tell who they serve.