A photograph is usually looked at but seldom looked into. Words and pictures can work together to communicate, more powerfully than either alone.
Stereophotography is where two photos are taken side by side at the same time usually about eye distance apart. By printing these two photos side by side at a certain size they can be viewed with an optical viewer which allows a person to see the left image with the left eye and the right image with the right eye. The brain translates both images into one 3 dimensional image showing depth of field just like your normal way of viewing things allows you to see and judge distance.
Below you will find a few examples of both Stereophotos and Stereo viewers both old and new.