Using a technique I used much as a journalist, I went to the World's Fair and if I saw an interesting looking person I went up to them and asked if I could take their picture.
Without fail, they said yes.
I took one before they were ready, one as they posed and one after they thought I was finished. At the end, I thanked them told them my name was Geoff and they told me their first name. We then wished each other well and moved on.
I guess in the last analysis, it's in how you ask.