Light traveled through a piece of glass, a lens you could screw off the camera. Hold the lens a foot or two away, and the image flipped.
The lens was attached to a box that had a shutter you opened and closed to let in the light. You could vary the time it was open. You could vary how large the opening was.
The light was focused on film, a strip of plastic (originally a wet concoction of cellulose and other stuff to make "dope"), that reacted to the light. High school kids could hang out in dark rooms developing film (and a finer sense of anatomy).
The whole process was tangible. (That the dark room featured a red light added to the, um, tangibility.)
For kicks you could make a shoe box pinhole camera, and take interesting photos with unreal depth of field. Cool and cheap, when cheap was cool.
So what does this have to do with today's media savvy tween digerati set?
First, though, all you young'uns who never saw a pinhole camera before need to gather a toilet paper roll, a piece of waxed paper, a piece of aluminum foil, anda couple of rubber bands.
(No, you can't do this digitally...you get to use all 10 fingers for this. Too clever by half....)
Put a small hole in the foil, attach it to one end of the tube, with the hole centered. Fold the waxed paper over the other end. Yep, use the rubber bands to hold it all together.
Point the aluminum side at a bright light source, focus on the waxed paper screen, and tell me what you see. Move it around a bit, what happens?
[OK, for those who cannot help themselves, I'll save you the trip to Google--you wil see an upside-down image that moves oppositee to the direction you move the camera.]
That's the observation, now here's the question--how can an image flip if there are no lenses? What can you infer about the property of light (at least here in our Newtonian sensate universe)?
And I will leave this open for now....