When a FAX is received, the header you see is part of the image. As such, it ends up in the TIFF file as part of the image. It is not available as ASCII/Unicode text at the receiving end. The only way to make it available as text would be to implement OCR. For various reasons, of complexity speed and accuracy, doing that inside the FAX software would not be a good idea.

The only information sent between the FAX machines as text is a 20 character identifier. The T.30 standard says this should contain digits, and it is usually set to the telephone number of the FAX machine. In fact, most machine can handle any ASCII characters in this identifier. The received identifier is made available by spandsp.