Upskirt Photos are a national issue for Japan?

Can one of my Japanese friends please help explain this article on illicit upskirt photos in Japan? Seen below is a warning poster from a subway in Japan.

…The loud shutter sound is supposed to deter voyeurs from taking sneaky pictures up women’s’ skirts — or down their tops. In Japan, upskirt and downblouse shots have become increasingly popular with the advent of high-resolution camera phones. As a result, all cell phones sold in Japan make a conspicuous shutter sound, or say the word “cheese” when a snap is taken…