Primer
How to authenticate a digital photograph, document, or video under FRE 901(b)(9), survive Daubert scrutiny, and establish chain of custody using SHA-256 + blockchain anchoring. Written for claims professionals, litigation counsel, forensic engineers, and risk managers handling evidence-dependent disputes.
When a photograph, PDF, or video file is introduced as evidence, the question isn't whether the file can be opened — it's whether the file in front of the court is the same file that was created at the time and place being claimed. Traditional digital evidence workflows rely on metadata (EXIF, file-system timestamps), custodial testimony, and hash values that match between collection and presentation. Each of those has failure modes. Metadata can be edited by any user with file access. Custodial testimony can be challenged. Hash values only authenticate the file if the original hash was recorded somewhere independent and tamper-evident.
Blockchain anchoring solves the "somewhere independent and tamper-evident" problem by recording the SHA-256 hash on a public ledger that thousands of independent parties keep a copy of.
Federal Rule of Evidence 901(b)(9) authorizes authentication by "evidence describing a process or system and showing that it produces an accurate result." The rule was written generally — the drafters in the 1970s could not have anticipated cryptographic hashing — but it applies cleanly to SHA-256 and blockchain anchoring:
The Daubert standard (Daubert v. Merrell Dow Pharmaceuticals, Inc., 509 U.S. 579 (1993)) asks four things of expert methodology:
Chain of custody requires documenting that evidence has not been altered between collection and presentation. A cryptographic timestamp anchored at the moment of collection provides a tamper-evident baseline:
The most commercially significant application in insurance is pre-loss documentation. The policyholder or an inspector documents an asset's condition before any loss event — photographs, measurements, inspection reports. Each file's SHA-256 hash is anchored to a public blockchain at the time of documentation. When a claim is filed, the on-chain record proves the photos existed at that earlier time. The evidence predates any incentive to fabricate.
In contested claims, this shifts the evidentiary burden. An opposing party alleging post-hoc fabrication must explain how a file with an on-chain hash recorded before the dispute could have been forged.
ProofLedger anchors each file's SHA-256 hash to both the Polygon blockchain (for instant confirmation at low cost) and, via daily batched Merkle roots, to the Bitcoin blockchain (for maximum immutability and widest judicial recognition). Every proof has both anchors; the user cites whichever is more persuasive in a given venue.
Verification is independent. The open-source verify-proof Python package
(pip install verify-proof) performs verification offline — hashing the file locally and checking
against the on-chain record — without any connection to ProofLedger's servers. Opposing counsel can run the
verification themselves; so can an expert witness, a judge's chambers, or any third party. A public REST
endpoint (documented here) is also available at
GET /api/v1/verify?hash=<sha256> for quick third-party lookups; for court-submission
contexts the offline package remains the authoritative path, since it does not depend on ProofLedger's
infrastructure being online.
Dual-chain anchoring for claims adjusters, attorneys, forensic engineers, and risk managers. Your files never leave your machine; only the hash goes on-chain.
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