On her website FAQ document examination expert witness Emily J. Will, D-BFDE, answers the question:
Q. Can a document examiner work with photocopies of questioned documents?
A. This question must be answered on a case by case basis. If the copy is of good quality, and if there is enough information in the writing to allow an opinion, a copy can be sufficient. But there are some situations where the opinion rests on a subtle aspect of the writing that might only be visible on an original viewed under the microscope. In such situations, examination of the original is critical. Often the examiner’s opinion must be qualified due to limitations on the examination process due to submission of non-original documents.