Facsimile (Fax) a method of encoding data, transmitting it over the telephone lines or radio broadcast, and receiving hard (text) copy, line drawings, or photographs.

A fax machine scans an image, whether it be text or a photo, by reading a very small area of the image at a time. The fax machine decides whether the area it is reading is light or dark and assigns the area a number such as "0" for white and "1" for dark. Then the fax transmits the number to a remote facsimile receiver (usually via telephone lines). The receiver makes a mark on paper corresponding to the area on the original image.

This process continues as the transmitting machine scans a series of small areas horizontally across the image, and transmits that information to the remote receiver. The transmitting fax then scans the next lower line and so on until the entire image has been scanned, digitized, and transmitted