How does a tiny hole create a full image of the world? A pinhole lets through only a narrow set of light rays from each point in a scene. Those rays land on a screen and form a picture. You build a viewer from an empty cereal box. Cut a flap in the front and tape waxed paper inside as a screen. Poke a single hole in the bottom with a thumbtack. Seal all edges so no stray light leaks in. Hold the box up to your face on a sunny day and look at the waxed paper. The scene appears upside-down and reversed. Make the hole bigger and the image gets brighter but blurrier.