The first close-up photos of Mars were taken with an analogue TV-camera and sent to earth as a grid of numbers. Each number represented a colour so scientists painted by numbers to colourize Mars in 1965. h/t @mwichary
In the 1960s, Eduardo Joselevich and Fanny Fingerman developed a technique to represent images with only four symbols. Full blocks or circles, in either black or white. They called it Fototrama and it was used at Olivetti and Philips for example.