I found a proper and informal method to add a description to an image,

  1. figcaption
  2. emphasis after a line break
two cats play-fighting on a bed
One play-fights, the other often takes it too far.

two cats lying on a bed, one resting its head on the body of the other
However, they still trust each other to snuggle up.

Alas, markdown has no code for captions, _nor_ does it work inside an html container.