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The images, taken by an unknown photographer, focus on the daily life of soldiers in the trenches.
French soldiers pose outside their shack, called "The Chalet," at la Sapiniere near Lachalade on the Argonne front, eastern France.
A viscount in the Armored Cavalry Branch of the French Army left behind a collection of hundreds of glass plates taken during World War One that have never been published until now. The images, taken by an unknown photographer, focus on the daily life of soldiers in the trenches.
French General Emile Eugene Belin, right, visits the front line near Arras, Northern France, in an undated photo.
The photographs were found by a Reuters employee who remembered there were suitcases full of stereoscopic glass plates from WWI in her family's home.
A French soldier aims an anti-aircraft machine gun from a trench at Perthes les Hurlus, eastern France, in an undated photo.
2014 marks the 100th anniversary of the start of WWI.
Field Marshall Douglas Haig rides a horse at an unknown location in France, Feb. 14, 1916. Haig was the British commander-in-chief during the Somme battle.
French cyclists of the Cavalry Corps, on the Champagne Front, Eastern France, Sept. 22, 1915.
French soldiers fire a 155 mm mortar from a trench on the front line, at an unknown location in France.
French soldiers stand in German trenches seized after being shelled on the Somme front, northern France in 1916.
Iinjured soldiers arrive at a hospital before being evacuated on the Champagne front, eastern France, in an undated photo.
Captured Germans soldiers march through Chalons en Champagne, Eastern France, in September 1915.
German soldiers, captured during the Battle of Verdun, take off their clothes for a body search by French soldiers, in Eastern France, in an undated photo.
A French soldier poses after taking a shower, at the rear guard near the front line, at an unknown location in France. The placard reads "Thermal complex of the Poilu, showers, massages, chiropodist, manicurist. Free massages for women."
Soldiers attend an entertainment show at Suippes, on the Champagne Front, Eastern France, in 1915.
French troops from the rear guard eat lunch near Arras, Northern France, in an undated photo.
French soldiers pose in a trench at Suippes on the Champagne front, eastern France, in an undated photo.
A French officer stands near a cemetery with recent graves of soldiers killed on the front lines of WWI, at Saint-Jean-sur-Tourbe on the Champagne front, eastern France, Dec. 19, 1916.
Read more about the discovery and view stereoscopic images on the Reuters Photographers Blog.