How to calculate Real World Object Size?

Question

I am taking image from camera. So i want to get object original width and height.For that I am using UIImagePickerController.

e.g If 15 inch monitor is placed on table. so when I took image from camera then i
want orginal size i.e. 15 inch. Does anyone have idea ? how can i achieve this ?.

EDIT I dont't want image size. I want actual object size....

EDIT 2 I want this type of app:-https://itunes.apple.com/us/app/easymeasure-measure-your-camera!/id349530105?mt=8

Thanks In Advance....

Answer 1

what you are asking for is not possible to determine with only a picture from a camera, acquiring the actual size of an object through a picture cannot be done without some other information telling you how far away the object is (which the camera cannot tell you).

edit: well actually not impossible to determine, bad choice of words... just very difficult. (vuforia augmented reality for example can determine the distance away an object is from the camera, but the object recognition is done as a preprocess and not just any old object)