Juries are generally allowed to examine enlarged photographs of the writing, and sometimes to see it under the microscope, but even when so doing what they see unexplained cannot be appreciated intelligently and unless taken for granted as meaning something which the experience of the expert who gives the opinion understands, and which they without such an education, could not be expected to understand that which the photographs show and the microscope makes visible is just as likely to be misleading as otherwise.
An expert may testify as to the characteristics of the handwriting in question; as to whether the writing is natural or feigned, or was or was not written at the same time, with the same pen and ink, and by the same person, and as to alterations or erasures therein; and as to the age of the writing and obscurities therein; the result of his examination of the writing under a magnifying glass; and to prove in some cases the standard of comparison.
In the United States a witness may be asked to write on cross-examination, but not in direct.
Before a paper can be accepted as a standard of comparison it must be proved to be genuine to the satisfaction of the judge. His decision on this question is final if supported by proper evidence. In some states the question of genuineness is for the jury.
A party denying his handwriting may be asked on cross-examination, if his signature to another instrument is genuine. This is the test which may be successfully applied to ascertain if the signature is genuine. A plaintiff, on one occasion, denied most positively that a receipt produced was in his handwriting. It was thus worded, "Received the Hole of the above." On being asked to write a sentence in which the word "whole" was introduced, he took evident pains to disguise his handwriting, but he adopted the phonetic style of spelling, and also persisted in using the capital H.
The practice of thus testing a witness is vindicated by one of the most sagacious of German jurists, Mittermaier, on grounds not only of expediency, but of authority.
Comparison of handwriting, either by jury or witness, is uniformly allowed to prove writings which are not old enough to prove themselves, but are too old to admit of direct proof of their genuineness.
Handwriting, considered under the law of evidence, includes not only the ordinary writing of one able to write, but also writing done in a disguised hand, or in cipher, and a mark made by one able or unable to write.
The principles regulating the proof of handwriting apply equally to civil and criminal cases.
The paper the handwriting of which is sought to be proved by experts must ordinarily be produced in court, but such production will be excused when the paper has been lost or destroyed and when it is a public record, which cannot be brought into court.