Device for encoding and marking of documents for identification and retrieval

A device which collects the pixel information generated during printing or scanning of a document, and transforms this sequential information into a code A which has a one-to-one relationship to the sequential pixel information, and which device computes from this code A a hashcode H which meets the requirements of a digital signature, and which device then feeds the digital information needed to print the hashcode H to the printer, in a pixel format, or feeds the same hashcode H to the digital media storage device, in both cases in a part of the document page which is digitally stored or printed, a method of use of the said device in encoding a document to form a hashcode H in pixel form.