Choose an image you have taken that have a good amount of depth in it.
You will be printing the same image 3-5 times as a 5x7.
Define each level of depth... what is the closest to the lens? Middle ground? background?
Then for each level, use an Xacto knife to precisely cut around each different depth.
Once you have all the layers cut in order from closest to the foreground to further back, use permanent mounting tape to place the images in order of depth.
Materials:
Here is a visual example done by a very talented student:
The part closest to the lens is the furthest from the background!