https://saitoha.github.io/libsixel/

Sixel was first introduced as a way of sending bitmap graphics to DEC dot matrix printers like the LA50. After being put into "sixel mode" the following data was interpreted to directly control six of the pins in the nine-pin print head. A string of sixel characters encodes a single 6-pixel high row of the image.

https://www.reddit.com/r/commandline/comments/4qyb90/netsurf_a_graphical_browser_on_xterm_using_sixel/

Running netsurf over sixel.

https://github.com/hpjansson/chafa

A command-line utility that converts all kinds of images, including animated GIFs, into sixel or ANSI/Unicode character output that can be displayed in a terminal.