I might be really wrong and probably legislation is different in each country but:

Giving someone a picture, film, audio or whatsoever media allows that person to have it, but not to broadcast it in any way (including internet).

It's different if you're in a public place, like streets, countryside, etc. then your image can be used (example: pictures of a demonstration or the queues for concert tickets, etc).

The naughty pictures of a girlfriend / wife are not broadcastable (is that a word?) since you don't have the rights for her public image.

When I worked in porn we were dead serious about it, to the point of -almost- being sued for not blurring the plate number of a passing-by car in a street scene.

About avoiding potentially embarrassing things, I don't think it's a valid argument. We all do silly stuff. We all make mistakes. We do things that are not silly nor mistakes, but years later we look at them in other way. Sending your years-long boyfriend a topless pic because you miss each other and are horny is perfectly right. If that couple breaks years later, posting that pic in hate is totally wrong.