Brian, the situation you witnessed is one of those cross cultural things. I think here though, parents know it's not the done thing to photograph other people's kids. And yes I am a parent, but I am also a photographer, and if I'd had the opportunity to go up to the girl's parents right after shooting, I certainly would have done. Just no supervising adults anywhere in sight.
Perhaps he thought because he was outside Japan, conventions that applied at home, didn't in the US. or maybe lived in the countryside of Japan, where everything is a bit more lax. Sorry, I know you didn't say he was specificly Japanese. But some things are 'Asian Things'.....
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Interesting, I was shooting an overhead pedestrian bridge the other day, it has frosted glass panels on the side which distort the shadows of people using it. This is a bridge between two buildings. A 'security guard' indicated that I wouldn't be able to take any more photos, because it was 'private property'. I was standing on the pavement at the time.
I indicated that I would stand in the road, and continue to take photos. I just waited until he wandered off. A part of me just wants to ask him quite innocently 'what time do you finish work?'.....he would nod and understand
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thus far I've sent copies of a similar shot (same girl but back to the camera - the way she is dressed is totally unique and beautiful) to a couple of the organising staff at the club, hoping that they might draw a result, but nothing yet.
Facility is a private members sports club, it was open to the paying public on that day, no help there. I might be able to make discreet enquiries thru the FB event page, I just realised.