A pinhole camera is a simple structure consisting of a light-proof container without a lens but a small aperture (hole) in one side. When taking a photo, light from a scene passes through the aperture, projecting an inverted image on the opposite side of the box eg the camera obscura effect. Due to the aperture being so small, it bends the light in a manner that inverts the image. Not only is it upside down, it is also a reversed image.
I really enjoyed creating our own pinhole cameras using chocolate powder, teabag and phone containers as the basis. We cut a square hole into the centre of a piece of card before taping a piece of aluminum foil over it. We then poked a tiny hole into the foil, blacked it out with some tape to prevent any light entering our cameras and then it was time to try them out!