When should I use Inverse Camera?

Inverse Camera is the feature that computes a Camera’s focal length and sometimes principal point and format size. It is used when you don’t know the camera parameters (usually when all you have is the photo prints or negative but not the camera). To use Inverse Camera you do need to know something about the scene – either Constraints,¬†known XYZ Control Points or be using Shapes (which are like automatic constraints).