One day when I was maybe nine years old, I was in the very back, what we called the “way back”, of the family station wagon. An empty box was next to me, so I put it over my head, as any bored nine year old boy might do. The day was bright, and the box had a small hole in one side, and so it was that I happened to create a pinhole camera (or camera obscura) by accident. It was one of the most magical discoveries of my life. Projected on the dark inside of that box was a blurry upside-down color image of the moving world outside. If you’ve never seen a pinhole camera in action, it really is amazing to behold, mostly because it is so utterly unexpected. All the more so when you’re a nine year old boy with no notion of why this should be.
If you want to see what it looks like, here’s the story of an artist who built a camera obscura on wheels.
You see this and you start to understand why the word “camera” comes from the Latin for “room”. To think that a big box with a hole in the side makes a passable real-time video monitor is so wonderfully strange. The basic principle of photography seems so simple when you start here.
Rambles Blog at Star Chamber 
When I was 14, I did photography like this using a pin hole camera and 8×10 photo paper in a cardboard box. Because the box was small (and I couldn’t fit inside), it was a single exposure camera. It only worked on really bright days. I would go into the dark room, load the paper, then put something over the pin hole and head outside. I would set down the box (camera), point, and shoot (remove the pinhole cover for between 20 seconds and a minute). Then, it was back into the dark room to develop and then reload the box.
I learned a lot of practical optics and physics that summer. The smaller the hole, the more crisp the image, the better the diffraction. The downside of the small hole was you need longer exposes to get the image. Of course, the image you get is also a negative, so it looks very different and unexpected when you finally develop it. Thanks for the reminder Ned, this brought me back.