Breaking an image up into lines is similar to how television cameras/displays and raster scan CRTs operated (IIRC TV dated back to the 1920s?), though wrapping the image on a drum was clever and not found in television technology. I wonder how they synchronize lines between the transmitter and receiver though (all video standards have hsync pulses, while I didn't see any such here). I'm not sure how fax machines worked/work either.