Optical-coherence-tomography-based algorithm for handwriting forensic analysis

摘要

This work describes a new method for handwriting forensic analysis using optical coherence tomography (OCT) images.The region of interest (ROI) in documents signature to be analyzed were pre-selected with a traditional optical analyzer(Docucenter 2000 – Projectina?) equipped with different wavelengths light sources and bandpass filters coupleddetector. The ROI where then submitted to OCT to 3D imaging (OCP930SR, Thorlabs Inc.) with optical resolution of6.0 microns. One original and 5 falsified signatures were produced by 5 different individuals, using a block of 5 sheets ofwhite sulfite paper A4 size and weight of 75 g/m^2, using the same blue ballpoint pen and in the same surface. Forpressure pen calibration, were developed a system computer controlled to maintain the pressure constant during writinglinear traces, 15 different pressure configuration were applied to each linear trace, resulting in a relation betweendeformation and applied pressure. An autonomous algorithm was developed to make surface detection, across OCTtomographic images, correct the paper surface curvature, detect and measure deformation on paper due to pen pressure,generating a new image in false color from differential pressure, based in previous calibration. This new image can beconsidered as a “fingerprint pressure” signature. This methodology may assist the forensic expert in correctlydetermining the authorship of a signature.