Thacher's Island lights--south tower / phot. by Hervey Friend, 77 Front St., Gloucester.

Stereographs are devices capable of building a three-dimensional​ image out of two photographs that have about two and a half inches difference between them so that it could imitate the two eyes’ real field of view. Combining these images into a single one with the help of stereoscope, a person can experience the illusion of the image’s depth. Stereoscope uses the same principle as in human binocular vision. Our eyes are separated by about two inches, so we see everything from two different angles. When the brain combined those views in a single picture, we get the spatial depth and dimension. Stereographs were extremely popular between 1850 and 1930 all around the world. Millions of stereographs were made during that time. There was a broad range of themes: landscape, travel, historical moments, nature disasters, architecture and many others. Nowadays, simply launch this collection full screen and put your mobile device in Google Cardboard Viewer.

The collection/dataset uses media from the world's largest public domain source Picryl.com. It is made in two steps - first manually picked, and then, found semi-automatically, with aid of image recognition, it comprises of more than 5,000 images. Everything in the collection is in the public domain, so there is no limitation on the dataset usage - educational, scientific, or commercial.