Chain of custody is the documented, unbroken record of how a piece of evidence was handled — who collected it, who held it, who accessed or copied it, and how it was protected — from the moment it was captured to its use in a proceeding. For surveillance footage it is what lets a clip stand up as evidence: a court needs assurance that the video presented is authentic, complete, and unaltered since recording, and the chain of custody is the proof.
In a video system it is built from several controls working together. Accurate, synchronised timestamps anchor when events occurred; secure storage and access control limit who can touch the footage; an audit trail records every view and export; and integrity protection — a hash or digital signature on an export — proves the clip has not been edited since it left the system. A defensible export carries its own provenance: original timestamps, a verifiable signature, and a record of who exported it and when.
The pitfall is breaking the chain through careless handling. Footage copied to a USB stick with no signature, passed hand to hand with no log, or taken from a system whose clock was wrong invites a challenge to its authenticity — and once the chain is broken it usually cannot be repaired. Plan for evidentiary use before an incident: synchronised time, locked-down access, full audit logging, and signed exports, so that when footage is needed as evidence its integrity is already provable rather than argued after the fact. This is engineering guidance, not legal advice — confirm specifics with qualified counsel.
