It seems like there are two choices here. I know which one I would pick.
The first choice is paranoia. Look everywhere and anywhere. When you go into the bathroom, look under the seat, look at the ceiling, look at the paper holder. When you go into an elevator, look up and try to find the camera. When you walk into your friend’s house, see if you are being taped.
The first choice will make you a nervous wreck, and because you will likely never find anything anywhere, you will become crazy with paranoia.
The second choice is to do nothing. Wash your hands and leave. Worry not about what crazies are out there – because they’re not significant or relevant to your life. Did this camera affect her or her son’s ability to pee?
The woman’s mistake was profound. What she should have done is detached the iphone in question, turned it off, and put it in her purse. Later, at home, turn it on, copy all the files to your own PC (for evidence) and wipe it back to factory. (This is the “finders keepers” philosophy.)
If the owner of the phone (who presumably was the voyeur) called the number to check on his phone, well, let’s just say that’s a conversation that would be fun to have in the presence of a policeman.