Controlling the camera through phone keys
There are many apps. You can go with Vosco which is my favorite one but without key mapping (no hardware button to take pic) but a great one. Otherwise, Camera360 is a good choice. Also you can go with CameraMx (or Mx Camera maybe) or Line Camera or Cymera (this one has a great range of photo editing tools as well). All of these can be customized to take pictures with volume key or so.