Did you know there’s a shortcut on the Lock screen to quickly open the camera? Swipe from right to left across the Lock screen. Bear in mind you can’t return to the Lock screen by swiping back the other way – you’ll need to swipe on the Home bar or press the Home button instead.
For security, if the Camera app is opened in this way, only the photos just taken can be seen; other items in the Camera Roll won’t be accessible.