This paper proposes a new service scheme which multiplexes several independent sub-documents onto the main document in a conventional facsimile broadcasting system. These multiplexed facsimile signals are moreover unified besides the voice channels in television system. The scheme does not increase the amount of facsimile signals, thus, it can save the frequency resources and communication channels. In this system, the main facsimile document is open for common subscribers, but the multiplexed sub-documents are delivered only for the special subscribers who are registered to the broadcasting station for each channel.

This paper presents a new digital signature scheme for computer-aided facsimile systems which directly embeds a signature onto document. We use multiple reference lines which have been scanned just before and modify each distance between changing pels both on the reference line specified by key and on the coding line with a single bit of the signature data. The sender embeds his signature secretly and transfers it, and the recipient makes a check of any forgery on the signature and the document. This scheme is compatible with the CCITT G3 and G4 facsimile standards. The total amount of data transmitted and the image quality are about the same to that of the original document, and thus an attacker may notice that no signature is embedded on the document.