An executed spy in France, with a sign above his head reading: “Spy – Traitor To His Country”. (Photo by General Photographic Agency/Getty Images). 1918

Dead bodies in the trenches, the results of German machine guns and shelling at the Hill of Cividale in Italy. (Photo by Hulton Archive/Getty Images). 1917

French soldiers combine gunfire with the throwing of rocks in an attempt to dislodge German soldiers from hillside trenches. (Photo by Central Press/Getty Images). 1916

British prisoners of war search the bodies of dead soldiers for valuables while a German guard makes an inventory. (Photo by General Photographic Agency/Getty Images). 1917

An unknown dead French soldier lying across German barbed wire. (Photo by General Photographic Agency/Getty Images). 1915

A French soldier's grave, marked by his rifle and helmet, on the battlefield of Verdun. (Photo by Hulton Archive/Getty Images). 1916

German troops advance across open ground at Villers-Bretonneux during Germany's last major effort to secure victory on the Western Front. (Photo by Hulton Archive/Getty Images). 1918

A German rifleman beside the corpse of a French soldier in a trench at Fort Vaux, France. (Photo by Hulton Archive/Getty Images). 1916

A dead British pilot lies on the ground next to the wreckage of his aircraft, looked on by German soldiers. (Photo by General Photographic Agency/Getty Images). 1915

Street fighting in Berlin between Government troops and Spartacists, during the Spartacist uprising which followed Germany's defeat in World War I. (Photo by Keystone/Getty Images). 1919

Three British guardsmen looking at the body of a dead German in a shell hole, after the Battle of Pilckem Ridge. (Photo by Hulton Archive/Getty Images). 31st July 1917

Dead French soldiers waiting to be buried. (Photo by Topical Press Agency/Getty Images). October 1915

Casualties who died covering the retreat of the 5th Army at Albert, during the German Spring Offensive of 1918. (Photo by Hulton Archive/Getty Images). Circa 1918

British soldiers in the trenches during World War I. (Photo by Hulton Archive/Getty Images). Circa 1914

The corpses of German soldiers lying amidst the debris in Louage Wood, during the Somme Campaign, World War I, 10th October 1916. (Photo by Topical Press Agency/Hulton Archive/Getty Images)

A Serbian soldier visits the grave of one of his colleagues in a field full of the graves of soldiers killed during the Austrian bombardment. (Photo by Topical Press Agency/Getty Images). September 1915

A memorial to the war dead at St Judes, Hampstead. (Photo by Topical Press Agency/Getty Images). August 1916