Determination of the sequence of line crossings by means of 3D laser profilometry

Abstract

The determination of the sequence of line crossings is still a current problem in the field of forensic documents examination. This paper presents the potentiality of the 3D micro-topography to resolve the writing order of signatures (if partially superimposed), to detect the tampering of manuscripts (if the added inscription superimposes itself on parts already written), to analyze pressure variation, and to identify strokes in handwritten. The system used, in this paper for creating 3D micro-topography, is based on conoscopic holography. It is a non-contact three-dimensional measuring system that allows producing holograms, even with incoherent light, with fringe periods that can be measured precisely to determine the exact distance to the point measured. This technique is suitable to obtain 3D micro-topography with high resolution also on surfaces with unevenness reflectivity (which is usual on the surface of the handwritten document). The proposed technique is able to obtained 3D profile in non-invading way. Therefore, the original draft do not be physically or chemically modified, allowing the possibility of multi-analysis in different time, also in case of forensic analysis with the necessity to preserving the original sample. The experiments performed with line crossings data base show that the proposed method is able of "positive identification" of writing sequence in the majority of the tests. When we have not had a positive identification, the result has been "inconclusive". The proposed technique, if correctly used, does not supply "false positive" or "probable" identifications. The possible results are only: "positive identification" and "inconclusive".