This post will tell you how to insert an image or photo from your gallery in to your 3d scene. This feature will help you use the image as a cutout or background.
1) Use the Image option under the menu as shown in the screenshot below.
2) Once you add the image, you can see it as a 2d plane and you can scale it to the level which covers the entire screen.
3) Now you can add characters and other object in-front of the 2d layer so that it looks like a whole new world in the camera.
Some quick examples are given below.