A COMPLEXITY MEASURE OF HANDWRITTEN CURVES - MODELING OF DYNAMIC SIGNATURE FORGERY

It is generally accepted that highly unstable and easily imitated signatures are among the main causes of deterioration in handwritten signature verification system performance. This work represents an original attempt to estimate, quantitatively and a priori from the coordinates sampled during its execution, the difficulty that could be experienced by a typical imitator in reproducing both visually and dynamically that signature. To achieve this goal, we first derive a functional model of what a typical imitator must do to copy dynamically any signature. A specific difficulty coefficient is then numerically estimated for a given signature. Experimentation geared specifically to signature imitation demonstrates the effectiveness of the model. The ranking of the tested signatures given by the difficulty coefficient was compared to three different sources: the opinions of the imitators themselves, the ones of an expert document examiner, and the ranking given by a specific pattern recognition algorithm. An example of application is also given.