A certificate names the work, the signer, and the object.

A useful certificate is not a compliment. It is the set of facts that let someone, years on, tell this work from a copy.

• Title, year, medium, and dimensions
• The artist's public name, and a check that the signer is that person
• Official images of the work
• A date, and a dated note if anything is corrected later
• A way to find this certificate again, not only a file in an inbox

A scan does not show whether the signer was checked. It does not stay with the work. It does not record who held it, or when it was handed back.

Stemma keeps three things apart: who signed, what the record says, and what is in your hands. A tamper-evident tag links the physical work to the certificate. A copied tag alone is not enough, because the work itself is checked too.

Signing does not move legal title. It is not an opinion about who painted the work. It records that a checked person signed this certificate, and that this object is the one the record names.

Artists and collectors still get paper certificates, or a scan of one. That scan is not a register. The same record can also hold a private collection file you give an insurer.