I just figured out how to categorise your images and there are two ways (none
automated, sorry):

- first one: update each and every "old" mirrors, this time choosing an
appropriate category

- second one: create/edit the winprofile.ini file located in "hts-cache"
folder of each mirror, and create/edit an entry called "Category=" (usually
the 2nd line) where it should be the name of your desired category. Next time
you make/update a mirror HTTrack will reorder your index page.

Note for shell users: in spite there isn't an option to create this file
(winprofile.ini) you may always create it manually with just one line
"Category=your_desired_category". Next time you mirror/update a website the
index file will be reordered.