title: UIImagePickerController: Detecting Camera button (shutter) pressed
body: <p>I would like to call a method that takes an NSNotification immediately after the user presses the camera shutter (i.e when the "Preview" tab bar has the buttons "Retake" and "Use"). </p>
  
  <p>I can't use the didFinishPickingImage method because at this time the user has already pressed the "Use" button. </p>
  
  <p>I have already implemented this by cameraOverlayView property of UIImagePickerController(see comments), but I wonder whether there are quicker ways of 'observing' this action. </p>
  
  <p>Any ideas?</p>