The contents of an official record or of a private record authorized to be recorded or filed in the public records and actually recorded or filed, if otherwise admissible, may be proved by a copy in perceivable form, certified as correct in accordance with Section 2902 of this title or testified to be correct by a witness who has compared it with the original. If a copy which complies with this section cannot be obtained by the exercise of reasonable diligence, other evidence of the contents may be admitted.