The common law best evidence rule requires that the evidence presented in court must be the original, unless the party is not able to do so; the court then can accept a secondary copy where it is satisfied that the original was lost, destroyed or otherwise unavailable in good faith. The common law best evidence rule is to ensure the integrity of a document.
This rule arises from a time before the advent of computers and photocopiers when all copying was done by hand. It is sometimes criticized as a rule that has outlived its purpose. In a world of computer and digital photos and documents, it is not possible to tell which copy is the original copy in many situations.
Section 31.2(1) of the Canada Evidence Act address this issue of best evidence rule involving electronic document. Section 31.2(1) reads as follows:
31.2 (1) The best evidence rule in respect of an electronic document is satisfied
(a) on proof of the integrity of the electronic documents system by or in which the electronic document was recorded or stored; or
(b) if an evidentiary presumption established under section 31.4 applies.
What this section says is that an electronic document will be deemed to be reliable as long as there is some evidence to support that the electronic system was in a proper working order when the electronic documents were generated.
Commonly, a lawyer trying to introduce electronic document in court will be required to call a witness or evidence in a form of affidavit to show the electronic system was in working order at the time the electronic documents were created. For example, the lawyer is required to call a witness to testify that when she took the screenshots of her text messages, her cell phone was in a proper working condition.