The pinhole camera (also called the "camera obscura") is essentially a dark box with a pinhole on one face, and a screen on the opposite face. Light reflecting off an object is directed through the pinhole to the screen, and an inverted image of the object forms on the screen. The caveat is that it is hard to see the image formed with the naked eye.
To be able to see the image, we will use a digital camera with a long exposure time (~1-30 seconds) attached to the pinhole camera. The optimal pinhole diameter is 1.9 * sqrt(f * lambda), where f is the orthogonal distance from the pinhole to the target surface and lambda is the wavelength of light (~550 nm). However, in the follow case, the suggested 0.1, 3, and 5mm pinhole sizes are used.