A contract with a signature the defendant denies, a will of disputed authenticity, an anonymous threatening note, a fraudulently completed cheque. In all these cases the question is the same: who wrote this? When it cannot be answered any other way, the answer is provided by handwriting evidence.

Handwriting expertise, also called forensic graphotechnics, is the means of evidence by which an expert analyses handwritten documents to determine their authorship, their authenticity, or the circumstances of their creation. Unlike classical graphology, which studies personality through handwriting, graphotechnics seeks to answer specific, verifiable questions. The expert compares the handwriting or signatures of disputed authorship with undisputed handwriting samples from the subject, and issues an opinion: of positive authorship, negative authorship, or indeterminacy. They can also establish whether a document has been altered or forged, or whether a signature was made under coercion.

This evidence is especially relevant in several offences. In documentary forgery it plays its greatest role, since the Criminal Code criminalises the alteration of documents and the impersonation of signatures. In document-based scams and frauds, where the deception takes the form of forged contracts or cheques. In challenged holographic wills. In threats and harassment in writing, where the expertise compares anonymous notes with samples from the suspect. And in contractual or employment disputes over documents signed in blank or under pressure.

The handwriting expert’s methodology follows several steps: obtaining sufficient and varied undisputed samples, since a single example of a signature is insufficient; analysing the questioned document, both macroscopically and microscopically, sometimes with infrared and ultraviolet techniques; and the systematic comparison that leads to the opinion.

It is worth knowing its limitations. The main one is the natural variability of handwriting: no one writes exactly the same way every time, which can make writings by the same author appear different. The second is the possibility of deliberate imitation by skilled forgers. The third is the insufficiency of undisputed samples. For all these reasons, handwriting expertise never reaches the certainty of DNA analysis, and a court that convicts solely on the basis of a medium-probability opinion may be violating the standard of proof beyond all reasonable doubt.

Faced with an adverse handwriting report, the defence may propose its own handwriting expert to produce a counter-report; challenge the methodology of the prosecution’s expert in cross-examination, examining whether they had sufficient samples; and point out the inherent limitations of this evidence to generate reasonable doubt, especially when the opinion is of medium probability.

Despite digitalisation, handwriting evidence remains fully relevant: many documents are still signed by hand. Moreover, a new modality has emerged, the analysis of biometric signatures on tablets, which examines dynamic parameters such as the speed and pressure of the stroke. When the experts of both parties reach opposing conclusions and both are well-founded, that contradiction can generate the reasonable doubt which, by in dubio pro reo, leads to acquittal.