Is it legal to take upskirt photos

Some weeks ago me and a friend who produces videos in Japan went to have lunch for a business meeting inside a crowded shopping mall. During our search for a Sushi place we rode the escalator up to the fifth level. What I did not know: while we rode the electric stairs my friend placed his iphone on his knee to take upskirt footage of two office ladies standing in front of us. They were certainly worthy of looking at them. However, he insisted on showing off and explaining to me what he was doing. I was slightly surprised and mildly offended. Why would he brag about that in public? The sexy office ladies looked at us and appeared to be shocked. Obviously, they understood English very well. They threatened to report us to police and security. I made a promise to myself during this unpleasant situation: Never ever meet with pornographers again! The situation started to escalate and the ladies demanded to see his camera roll. He willingly showed it to them and none of their photos were on it. He had an application installed that would shuffle new images and videos to a hidden folder. The ladies were still not convinced, but let go with lack of evidence. Of course, such an unpleasant situation makes me think: how much veuyeur and upskirt content is legal? Is it legal to shoot and is it legal to earn money from such illicit snaps? Each country has their own laws. In essence it seems to be accepted as long as you can’t identify depicted people. The art of the trade is not to get caught. Getting caught can bear substantial fines and prison time since upskirting may be defined as stalking.