I was playing with image dithering both as an aestetic and a way to make images smaller recently, inspired by solar.lowtechmagazine.com and others.
I made these four as title images for the collapse blog post series using the following Imagemagick script:
convert image.jpg -resize 840x840 -strip -colors 4 -ordered-dither o8x8 image-dithered.png
Security has always been an excuse not to adopt SVG more (and even if it were, a new vector format could be introduced, but as you said it can be sanitized).
Video codecs also introduce security problems and they are one of the main attack vectors towards multimedia systems embedded in cars and more.