The J. Paul Getty Museum
Keystone View Co.
License, verbatimCC0
The J. Paul Getty Museum: image dedicated to the public domain under Creative Commons Zero (CC0), stated on the media record itself ('Rights for Media'), with download clearance.
Keystone View Co.. Fusing the upper pictures requires 3 1/2 prism diopters of Fusional Convergence. Changing Fixation from upper to lower pictures..., about 1930. The J. Paul Getty Museum.