Size difference - As you can see the trees and the shadows look smaller as they get farther away from me.
as you can see the images will get larger as they are closer to me and I have labeled the particular image i am talking about.
Occlusion - In this picture there is a box with a skull in front of it, as well as a mistifying skull in the back of everything. I can tell what objects are in front of one another and it is because of occlusion. This portrays depth because i can tell what object is closest to me.