What’s old is new again.
Back in the early Macintosh computer days, when the Earth’s crust was still cooling, getting photos and artwork to look presentable on these computers’ 1-bit monochrome displays was something of an art form.
Much of that know-how has fallen by the wayside as screens improved…but with wafer-thin, ultra-low-power 2- and 3-color E-Ink displays appearing everywhere now, a refresher in those techniques is suddenly relevant again.
A couple of software options are shown in this guide. ImageMagick (a free command-line tool) and Photoshop (not free, but many folks already have it).