Exporting CCTV evidence that stands up: hash, manifest and a clean trail

When something goes wrong at a shop, a branch or a junction, someone asks for the footage. Too often it arrives on a pen drive with a file name like VID_0042, and no way to show where it has been.

What makes footage evidence

Footage is only as good as your ability to show three things: that it is the right footage, that it is complete, and that nobody changed it.

A fingerprint of every file

An export gets a SHA-256 hash. Change one frame and the hash changes. Whoever receives the file can recompute the hash and compare.

A signed manifest

The manifest lists every file in the export with its hash, signed by the system that made it. A verifier tool checks the signature, so changing the list is as visible as changing a file.

A watermark

A visible watermark names the user, the time and the site. It discourages passing footage around, and it tells you whose export leaked if one does.

A record of who handled it

Every view, export and share of a case should be logged. That log is the chain of custody. See chain of custody.

The steps

1. Bookmark the moment with a note and tags.
2. Build a case from clips, snapshots, notes and the people involved.
3. Export with a hash, a manifest and a watermark.
4. Hand over with an expiring, password-protected link.
5. Keep a legal hold on the footage so it cannot be deleted while the case is open.

Evidence and Compliance does all five. The legal background is in what the Privacy Act, 2075 asks of CCTV operators.

Questions people ask

Why does a hash matter?

A SHA-256 hash is a fingerprint of the file. Change a single frame and the fingerprint changes, so anyone can check the file is the one that was exported.

What is a signed manifest?

A list of the files in an export with their hashes, signed by the system that created them, so edits to the list also show up.

Can I share an export without giving access to the system?

Yes. Send an expiring, password-protected, view-only link.