This is my own character smacking people at the bar, taken with my own camera.
Answer: You go to passive mode and find a "willing" NPC participant. You bring up the camera, and while you're in the normal camera screen you press L2. Your character will target the NPC and the camera will switch to 3rd person. It's as simple as that. You can only take pics from the back of your character while you're targeting someone, but if you walk away you can take pics from the front. If you walk out of the lock-on range the camera switches back to normal. You can punch by pressing R2 and L2 at the same time.
It worked for me once, haven't tried since. So I don't know if it was a fluke or if it works for everyone. Try it if you want.