Registered fax the document to be sent and the resulting multipage image is encapsulated in an electronic envelope file format that allows time stamp insertion as meta data or as a specific tag.<br> - This envelope document is digitally signed using non reversible cryptography elements and the signature is then printed on the last page of the document for facsimile transmission.<br> - The receipt of the fax acknowledgment and subsequent transmission report validates that the content has been delivered in full to the receiver, including the page containing the signature and informing the receiver about the certified nature of the facsimile transmission.<br>
Fax systems used direct conversions of image darkness to audio tone in a continuous or analog manner. Since the 1980s, most machines modulate the transmitted audio frequencies using a digital representation of the page which is compressed to quickly transmit areas which are all-white or all-black. Scottish inventor Alexander Bain worked on chemical mechanical fax type devices and in 1846 was able to reproduce graphic signs in laboratory experiments. He received British patent 9745 on May 27, 1843 for his "Electric Printing Telegraph". Frederick Bakewell made several improvements on Bain's design and demonstrated a telefax machine. The Pantelegraph was invented by