Image Processing: Near/Far Objects

Does anyone know of any techniques that make it possible to work out how close an object is to the camera (when the image was captured)?

In the case I am concerned with, it does not matter if the photographer used a zoom or not, nor does it matter what the exact distance is between certain objects in the image vs. the camera. All that matters is that certain objects can be classified as closer to the camera than other objects - I am not sure if this is even possible...

Answer 1

[Sarah]

Look into the "structure from motion" problem.