Image Scale Measurement

I need to obtain the scale measurement off of an images captured with a PTZ Sony EVI D30. I am not sure how this can be done, but I would think that you could get the measurement from the Lense (The Lense of the Camera has to know how far the distance is between the person and the camera. There might be other ways to do this. This camera is designed with a Serial Interface to communicate with a computer. RS232 Port. A real world example would be if I took a picture of my face and captured the image on a computer screen, I would want to know the "Real World Measurement" of say for example the distance between my eyes. Note this project doesn't include the capturing of the images. All I need is the algorithm to get the measurements between two mouse clicks expressed in mm with a tolerance of .5mm ## Deliverables Complete and fully-functional working program(s) in executable form as well as complete source code of all work done. Complete copyrights to all work purchased. ## Platform Must be able to run with a Sony EVI D30/D100 Camera on an XP Platform. ## Deadline information The software will be tested and must be within the tolerance in able to be a valid piece. A bonus will be paid for speed and accuracy.