Japan Travel Fixes
What should I know about photography and voyeurism laws?
Taking photos up someone's skirt, or secretly photographing someone changing or bathing, is a clear crime under each prefecture's public nuisance prevention ordinance — even first offenses are commonly arrested and prosecuted. Japanese-market phones can't have their camera shutter sound disabled specifically as an anti-voyeurism measure.
Photography in crowded trains or on escalators, where other people can end up in frame without meaning to, can also raise suspicion depending on how it's done, so it's worth being deliberate about what you're shooting.
See the culture and manners article for photo etiquette at shrines and temples and on private property — the difference there is that this is a crime, not a courtesy.