Patent US 6,571,001

A system for distinguishing photocopied or laser-printed documents from original documents produced by offset printing, handwriting, or typewriting. The system scans a document at low-resolution and at high-resolution to produce a low-resolution and a high-resolution matrix representation of the presence or absence of ink or toner at discrete locations on the surface of the document. Printed regions detected by the system at low-resolution are used to mask regions of the high-resolution matrix representation from the analysis. The remaining unmasked regions of the high-resolution matrix representation are analyzed by the system to detect discrete microdots uniformly distributed within those regions. The presence of microdots on the surface of the document indicates that the document was produced as a photocopied or a laser-printed duplicate.