This is the online site for the Boyd/Jordan collection of stereographs related to the Great War (WWI).  Stereoscopic photography was a popular pastime in the Great War period, and companies in most of the warring nations sold stereoviews. This web site describes the manufacturers of photographic stereoviews and explains how to identify them based on their markings. Scans of the actual images are also located within this site, as are check-list representing offerings from the various publishers.
https://www.greatwarin3d.org/