import pywikibot
from pywikibot import pagegenerators as pg

site = pywikibot.Site(fam="commons")
cat = pywikibot.Category(site, 'Category:Media_from_the_National_Museums_of_World_Culture')
gen = pg.CategorizedPageGenerator(cat)

for page in gen:
    filePage = pywikibot.FilePage(page)
    try:
        # Do something... E.g. add template for speedy deletion
        filePage.text = "{{speedydelete|broken file upload}}\n" + current
        filePage.save("Add template for speedy deletion due to no image uploaded, only text")
    except pywikibot.exceptions.PageRelatedError as e: # normally means there's no such page
        print("{} seems to not exist on Commons".format(filePage)