A true story
Before we were married, my wife and I took a train journey to Derby and back to Nottingham in the UK. I had taken pics of her flashing in public (but very discretely) over the previous weeks in various places. On the train, we were in a bay alone but with people the other side of the seats.
We kissed and fondled and I encouraged her to play with herself. She did and I moved back to give room to use the camera. I managed to get two pics of her reaching orgasm, with a stranger's head in the background, quite unaware!
Still have the proof and very sexy she looks too. Unfortunately not much like that has happened since.
(This was about 25 years ago)