Abstract: A signature to be verified is written on an area which carries horizontal and vertical lines using a pen. As the lines are crossed signals representative of the vertical and horizontal components of the pen tip velocity and whether the tip is in contact with the area are passed to a computer. A hidden Markov model derived from vertical and horizontal velocities and a "contact" signal occurring as a number of authentic signatures are written is stored by the computer. A forward pass of the Baum-Welch algorithm is used to calculate the probability that the vertical and horizontal components of the pen tip and the contacts between pen tip and the writing area could have been produced from the hidden Markov model. This probability is used to decide whether the signature is authentic.

Abstract: The forgery of signatures is made more difficult if the dynamic features of a signature can be checked when the signature is verified. Signatures to be verified are written with a pen which is sensitive to light received at its tip, each signature being written on an area having shading in intensity or color which varies with position. As the pen is moved a signal which depends on the light received by the pen varies in a way which is characteristic of the dynamic features of the signature. Verification is by comparing the time variation of the said signal with a previous authentic version as well as by comparing signatures. Comparison may be carried out automatically or by an operator who views a display of the authentic signal. The invention may also be used for data capture when characters are written on paper which has areas of different intensity or color of shading.