Step 1: 3D design + and pinhole
I won't go into detail on what a pinhole camera is but in essence, it is a simple camera with no lens but a small aperture (made with a pin) that projects an inverted image into the film. There are many factors to consider for the pinhole specially the diameter of the hole, the distance to the film and the type of film you are going to use. I found a website called MrPinhole that summarizes the most important features.
Step 2: Printing the STL files!
I uploaded the STL files for you to print and customize! Let me know how things turned out.