Peep box picture
Illustration for presentation in a peep-box, i.e. in an optical instrument for viewing images at the correct perspective distance. Special peep-box pictures were often produced as coloured copperplate engravings in the 18th century. As a rule, they were created upside down, as the optical device of the boxes, which were equipped with a lens and a mirror, meant that the image could be seen as a mirror image.