Heyguys.. This isn't exactly a programming question exactly. I just want to know what your approach would be to a common problem in Digital image processing.

Lets say you have an image of a a few trees in say jpg format. How would you go about finding the heights of each of these trees. The photo is the only input you have.

I want to know the approaches you have not code. So it doesnt matter if your answers are vague, or non DIP-ish.