It's unlikely that you'll be able to refrain from taking photos and videos at concerts however if you're going to take them, you may as well be as discrete as possible! This app allows you to take photos and videos without distracting people behind you.
The app shows a dimmed preview screen to minimize distraction for people behind you.
Scroll left and right to switch between camera and video modes. An icon at the bottom of the screen indicates which mode you are currently in.