In order to keep "junk science" out of the courts, the courts require expert witnesses to offer opinions that are supported by sound science. The trained document examiner is prepared to answer the question, "Why do you believe this is true."
Questioned document examination cannot state that a person is identified or eliminated as the writer of a document just because the writings look similar or different. Measurements are taken and compared between the known and questioned documents. These measurements are presented in understandable charts.
The document examiner collects enough samples of writing to determine the variability of the known writing. Using measurements, the document examiner determines whether the questioned writing falls within the range of the samples of known writing. This information cannot be determined with a simple visual inspection.
Each time a person writes, the letters and words are formed a little differently. The writer of a questioned documents can be eliminated only when enough samples of the subject's writing are collected for the handwriting analyst to learn these differences. This is why the document examiner will ask a client for as many examples of the person's known writing as possible.
Original documents are always better than photocopies. Original documents show all of the details, especially with handwriting. Photocopies have inherent distortion and stray marks on the page. The black copier toner obscures important details of the document.