METHOD AND APPARATUS FOR DETECTING PRINTED IMAGES ON DOCUMENTS BY TESTING FOR THE PRESENCE IN THE IMAGES OF STRUCTURAL ELEMENTS HAVING DEFINED REGULARITIES WHICH ARE RECOGNIZABLE BY THE EYE AND COMMON TO A VARIETY OF DOCUMENTS

In order to detect security documents irrespective of their individual graphic designs, a method and apparatus are provided in which the presence of certain structural elements common to a variety of different security documents are analyzed without analyzing the whole printed image or comparing it for identity with the stored printed image. For example, the structural elements may be curved colored lines present in a certain minimum density of a surface, or intertwined line structures known as guilloches. The document to be copied is scanned as in any normal copying operation and the structural elements identified by electronic pattern recognition in order to determine whether copying is to be permitted, without requiring additional detection elements.