3D reconstruction of an image based on depth of intensity levels?
This is an extremely difficult task, one which is a very active line of research. I've managed to find a semi-recent paper on the subject. I won't go into the details, but here's a few things that this paper found that can be used.


Textures: If you see a given texture, they can help you figure out how far something is away. The wood texture here would be quite ideal for this.
Fixed object sizes: Identify common objects, see how large they are, and use them to help with depth analysis. The phone book, soda bottle, etc should work well with this.
Focus: If you know how the picture was take, focus can help you identify ranges.
Shadows- If you know where the light was coming from, shadows can help you identify how tall objects are, and thus how far they are away.