How Authentication Services Detect Forgeries: Inside PSA, JSA, and Zarelli
The authentication process is frequently misunderstood by collectors who either over-trust its conclusions or dismiss it as subjective. Third-party authentication is neither foolproof nor arbitrary — it is a structured comparison process informed by extensive exemplar databases and forensic analysis. Understanding how it works helps collectors interpret authentication meaningfully.
The Exemplar Database
The foundation of handwriting-based authentication is exemplar comparison — comparing the signature being evaluated against documented authentic signatures by the same individual. PSA/DNA has processed millions of items and maintains the most extensive exemplar database in the industry. JSA and Zarelli maintain category-specific databases (entertainment/sports for JSA; NASA and space for Zarelli). Authentication quality is directly related to the depth of exemplar data for the specific signer.
What Authenticators Examine
- Letter formation — how each letter is formed, including pen lifts, start and end strokes, and connecting strokes between letters
- Pen pressure — where pressure is heaviest (typically beginning of strokes) vs. lighter (end of strokes)
- Speed indicators — experienced signers write quickly; forgers writing slowly leave different pressure and flow characteristics
- Proportions — the relative size of letters within a signature is consistent across authentic examples
Limitations
Authentication is professional opinion, not certainty. Skilled forgers who have studied exemplars can produce signatures that pass standard review. Authentication reduces risk; it does not eliminate it. For high-value purchases, authentication is necessary but not sufficient — strong provenance is the additional layer that authentication alone cannot replace.
