Optoelectronic system used to determine chronological sequence of line crossing

A difficult problem in questioned document examination is the determination of the chronological sequence of two or more writing media or other marks. If the questioned document contains an intersection between two lines, it can be important to know which of the lines has been produced first and, as a consequence, is older than the other. The determination of the order of crossing lines is appropriate in cases of suspicions that the content of a document has been altered at a later date by adding a part to it, for instance in a will or signed legal agreement (blank signature). Therefore, the determination of sequence of crossing strokes can provide important information when investigating a fraud. In this paper, we propose the use of a non-contact profilometer based on the conoscopic holography. The proposed profilometry is suitable to obtain 3D micro-topography with high resolution also on surface with unevenness reflectivity (this situation is usual on the surface of the handwritten document). Therefore the system leaves the investigated surface unaltered so that the questioned document can be studied by means of other destructive or non-destructive technique in different time.