PhotoModeler needs to know where the imaging medium (film or CCD) is placed relative to the camera lens and body at the instant of the exposure. With a digital camera or CCD video camera, the imaging sensor is fixed onto the body of the camera and as long as the lens position is fixed to the body also, you have a rigid and highly repeatable means of locating any individual CCD pixel in the lens / camera / media system.
On the other hand, in a film camera, the film is removed from the camera for processing and digitization. By the time we are locating points on the film image in PhotoModeler, we have little idea where that point was relative to the lens / camera body at the time of the exposure.