A major problem in automatic signature verification is the rejection of true signatures. One way of capturing a signature is to use a special pen 10 to write on an area 13 having horizontal lines, the pen being constructed to pass a signal to a computer 11 indicating whether the pen tip is in contact with the area 13 and when the lines in the area 13 are crossed. Signals characteristic of signatures derived in this way are analyzed and stored. To enable verification to be carried out a number of authentic signatures are analyzed and a number of measures such as means and standard deviations of signature features are determined and stored. When a trial signature is to be verified, the same features of the trial signature are measured and the results are compared with the stored measures. It has been discovered that many false rejections of true signatures are due to variations of certain types such as hesitations which occur when the pen tip is off the writing area between inked segments of the signature. The method of the invention allows for such time variations by, for example, modifying the measurements obtained from the trial signature to remove the effect of these variations if a rejection occurs and then comparing the modified measurements with the stored measurements to determine whether the trial signature can now be accepted.