In Canada, taking a pic of someone in her private home is a criminal offense. I have never heard about such thing in public place. However, you have to distinguish between simple public candid pic and trying upskirt pic (the latter is criminal I think).
I love taking candid pic. But never upskirt pic and never if I have a doubt the young woman could be under 18.
Living in a very touristic place, I have to say that I'm surely part of many "souvenir pics". I don't see what I could have said against it in a public place. I just try to avoid being on the pic
