I tend to save things I read as PDFs because it feels the most robust archival formal for the future.
How do you save images in plain text ? Lot of usefull information is stored in pictures. ie: in technical articles about graphics, hardware. Or some diagrams mentioned and refereced in the text. Even medieval books have pictures, because some things need to be shown, and it is not enough to just write some text about it.
Anyway, youre probably just a very very old troll, typing this on a typewriter...
Base64, like countless websites. Or just accept that you don't have to act like a lawyer with internet comments and simply save them as image files.
I mean, technically, we have 7000yo graphics, but they were really too low-res to be functional for archiving data.