On-Line Signature Verifier Incorporating Pen Position,Pen Pressure, and Pen Inclination Trajectories

This paper proposes a new algorithm PPI (pen-position/penpressure/pen-inclination) for on-line pen input signature verification. The algorithm considers writer’s signature as a trajectory of pen-position, penpressure and pen-inclination which evolves over time, so that it is dynamic and biometric. Since the algorithm uses pen-trajectory information, it naturally needs to incorporate stroke number (number of pen-ups/pen-downs) variations as well as shape variations. The proposed scheme first generates templates from several authentic signatures of individuals. In the verification phase, the scheme computes a distance between the template and input trajectory. Care needs to be taken in computing the distance function because; (i) length of a pen input trajectory may be different from that of template even if the signature is genuine; (ii) number of strokes of a pen input trajectory may be different from that of template, i.e., the number of pen-ups/pen-downs obtained may differ from that of template even for an authentic signature. If the computed distance does not exceed a threshold value, the input signature is predicted to be genuine, otherwise it is predicted to be forgery. A preliminary experiment is performed on a database consisting of 293 genuine writings and 540 forgery writings, from 8 individuals. Average correct verification rate was 97.6 % whereas average forgery rejection rate was 98.7 %. Since no fine tuning was done, this preliminary result looks very promising.