We begin by considering a camera, fixed in space, in order to first understand the response of the camera to light. Later (Chapter 6) we set it free again, to move, as it might in an actual eyetap system.
Please read carefully Chapters 4 and 5, and implement a CEMENTing of multiple pictures together to simulate the following: double exposure, long exposure, etc., as well as combining images in various proportions.
The best way to achieve this is to complete the exercise outlined in pnmpwadd.