In Latin, camera = room and obscura = dark. Simply explained, the camera obscura is an optical device that projects an image on a screen. The really cool thing about it is that you can make one yourself!
Turn a room into a camera obscura. Shut out all the light from a room by covering the window with a piece of card or hardboard, cut to fit. Bore a hole through the card or board. An upside down moving colour image of the scene outside will appear on a piece of paper held opposite the hole. Experiment with different sizes of holes and see the effect on the image.
Use a box! A portable camera obscura can be made out of a cardboard box. First, tape up the box to ensure that no light can penetrate it. Then cut away part of one end of the box and fix a screen of tracing paper across it. At the opposite end cut a 25mm hole in the box, cover this with kitchen foil, tape down the edges and bore a neat round hole through the foil that is no larger than the lead of a pencil. Take the box outside, or to a window, shutting out as much light as possible with a thick blanket. An upside down image of the scene outside will be seen on the screen!
* Instructions taken from this site.