If you'll darken a room--it doesn't have to be absolutely dark, tho that helps--then make a small hole in a shade opposite a blank wall, on the wall you'll see, projected in a circular upside-down image, what's outside. That's how a pinhole camera works. In the case of my old Kodak, it had a film-holder built in & the little red indicator hole on the back told me when I'd advanced the film sufficiently.
The technique is called 'camera obscura,' which literally translates 'dark room.' Those wonderful 'perfect-perspective' drawings in the 19th Century--& earlier--were made with a portable camera obscura. The US Corps of Topographical Engineers--the Army's mapmakers--used 'em all over the west. The guys called 'em 'the dammed ol' sweatbox,' but they were how those drawings were made. I did an article about 'em in Charley Eckhardt's Texas on texasescapes.com, but you'l have to scroll down a ways to find it. It was sometime in '07, I think.
The technique pretty much died out once portable photography became common. Sears, in the 1890s, sold a table-top version of a camera obscura as a 'sketchette,' & as late as the 1950s a version of it was being hawked to kids in comic-book ads. That one never worked very well because the need to exclude all light except that coming from the illluminated subject was never addressed by the device.
