You can take pictures without anyone noticing if you want. Just open the camera, then launches multitasking and hides through the various applications you have open, but do not go in them, when you want you can touch the button to turn up the volume and provide a photo.
But have the precaution to take the sound to the iPhone before, because although it does not show that you are in the application of the camera taking a picture sound is also emitted ...