This works possibly for all the zites.
You are admin of the zeronet site and you see its size grows => New visitors is asked to increase site quota and download tens of megabytes => not good.
open your zite; mouse drag & drop (0) corner button to the left to open its menu in which you click the "OPEN SITE DIRECTORY" link
open content.json and add following new line after for example line "modified": *,
alternatively to exclude all particular file types, no matter in which directory they are, try:
Sign and publish changes
files copied to data/img/, data/vid will no longer be force downloaded by all new site visitors but become optional (will be loaded once visitor request the page that contain them).
Related topic: How to create static site with big streamable vide0s