Presumption of document authenticity: courts may presume truth and handwriting unless rebutted and admit unstamped evidence. Where a document produced, seized, or received in proceedings under this Act or any other law is tendered by the prosecution against the person from whose custody it came or any person jointly tried with them, the court shall, unless the contrary is proved, presume the truth of its contents and that signatures or parts purporting to be in a particular person's handwriting are in that person's handwriting, including that executed or attested documents were executed or attested by the purported persons; the court must admit such a document even if not duly stamped, if otherwise admissible.