California Evidence Code
Nothing in this article shall be construed to limit the means by which a writing may be authenticated or proved.
(a) For purposes of this chapter, a writing shall include any graffiti consisting of written words, insignia, symbols, or any other markings which convey a particular meaning.
(b) Any writing described in subdivision (a), or any photograph thereof, may be admitted into evidence in an action for vandalism, for the purpose of proving that the writing was made by the defendant.
(c) The admissibility of any fact offered to prove that the writing was made by the defendant shall, upon motion of the defendant, be ruled upon outside the presence of the jury, and is subject to the requirements of Sections 1416, 1417, and 1418.
Except as provided by statute, the testimony of a subscribing witness is not required to authenticate a writing.
If the testimony of a subscribing witness is required by statute to authenticate a writing and the subscribing witness denies or does not recollect the execution of the writing, the writing may be authenticated by other evidence.
A writing may be authenticated by anyone who saw the writing made or executed, including a subscribing witness.
A writing may be authenticated by evidence that: (a) The party against whom it is offered has at any time admitted its authenticity; or
(b) The writing has been acted upon as authentic by the party against whom it is offered.
A writing may be authenticated by evidence of the genuineness of the handwriting of the maker.
A witness who is not otherwise qualified to testify as an expert may state his opinion whether a writing is in the handwriting of a supposed writer if the court finds that he has personal knowledge of the handwriting of the supposed writer. Such personal knowlegde may be acquired from:
(a) Having seen the supposed writer write;
(b) Having seen a writing purporting to be in the handwriting of the supposed writer and upon which the supposed writer has acted or been charged;
(c) Having received letters in the due course of mail purporting to be from the supposed writer in response to letters duly addressed and mailed by him to the supposed writer; or
(d) Any other means of obtaining personal knowledge of the handwriting of the supposed writer.
The genuineness of handwriting, or the lack thereof, may be proved by a comparison made by the trier of fact with handwriting (a) which the court finds was admitted or treated as genuine by the party against whom the evidence is offered or (b) otherwise proved to be genuine to the satisfaction of the court.
The genuineness of writing, or the lack thereof, may be proved by a comparison made by an expert witness with writing (a) which the court finds was admitted or treated as genuine by the party against whom the evidence is offered or (b) otherwise proved to be genuine to the satisfaction of the court.
Where a writing whose genuineness is sought to be proved is more than 30 years old, the comparison under Section 1417 or 1418 may be made with writing purporting to be genuine, and generally respected and acted upon as such, by persons having an interest in knowing whether it is genuine.
A writing may be authenticated by evidence that the writing was received in response to a communication sent to the person who is claimed by the proponent of the evidence to be the author of the writing.
A writing may be authenticated by evidence that the writing refers to or states matters that are unlikely to be known to anyone other than the person who is claimed by the proponent of the evidence to be the author of the writing.