Maintaining digital evidence longevity entails more than keeping a true copy of a digital object over time. The true copy also must retain its unaltered content in an unbroken chain of custody that addresses data preservation and the accuracy, reliability, and durability of the hardware and software systems involved.

From a legal perspective, meeting chain of custody requirements for a digital object is not any harder than, say, meeting those for DNA or for a bullet collected at the scene of a crime. The issue is one of certification rather than replication because ensuring the chain of custody for digital content does not involve an additional act of copying or physical transformation. It simply requires that any change in safeguarding the digital object must be authenticated and recorded in order for it to be introduced as evidence at a later date. However, this problem cannot be solved by digital means alone. It requires activity outside the digital realm that documents when a change of custody has taken place — or certifies it has not.

From: The Long-term Preservation of Digital Evidence by Arthur Gingrande