To be honest it happens all of the time. Kaos goes everywhere cause he's a service dog, and I live in NYC. Tourists that can't speak english do it ALL the time. I don't really mind though. The last time I had someone do it, they were tourists from Spain and they emailed me the pictures weeks later. I was grateful and surprised they did.
I am always weird about strangers touching him though, or even picking him up.
Otherwise I don't mind them taking pictures, I would take pictures if I saw him too.