How do I determine distance in a picture?

Question

With photograhy the police must use mathematical calcuations to determine the distance one object is from another. I have a picture with two objects that have the same height. These objects are separated by an unkown distance. How would I find the distance between the objects from a single picture knowing only the heights of the two objects?

Answer 1

If the two objects are a known height and either the same distance from the camera or each a known distance from the camera, it's easy, use the height of the boject just like a ruler to measure the distance between them. But if the objects are different unknown distances from the camera and eachother, there's really no way to figure the distance between them. There's too many variables with focal length and etc.

Answer 2

The math is done using a triangle. If you know the height of two of the objects in a picture, say a tree or building, you can use the formula
A(squared) +B(squared)=C(squared)
In other words, if you know the height and/or distance of two of the angles of an imaginary triangle in your picture, you can square them (times themselves), add them, and the result will tell you the length/distance of the third side of the triangle.
Hope that helped.