First up, the jpg should be traced to be an SVG. This can be done with Inkscape, and then the SVG can be processed with (for example) SVGOMG https://jakearchibald.github.io/svgomg/ to strip out as much unnecessary code as possible. People will be happy to help with this on the mailing list.
A few things to do with
clue.jpg
:epub:type="z3998:illustration se:image.color-depth.black-on-transparent"
, and should be wrapped with a<figure>
element.Ask if you need help with any of these steps.