National Library of Scotland posted a photo:
Four uniformed men pausing for a rest outside a large brick building. According to the original caption they are dispatch riders. Two men in shirtsleeves are sitting on a pile of logs, whilst the other two are leaning on their motorbikes. Three of the men are wearing steel helmets and the fourth is wearing a hat with goggles pushed up over the brim. It is a beautiful sunny day and the ground underfoot is dry and dusty.
Dispatch riders were used to relay vital messages between different areas of the Front. Their work was especially important when access to a wireless was not possible. Their work often brought them dangerously close to enemy fire.
[Original reads: 'OFFICIAL PHOTOGRAPHS TAKEN ON THE BRITISH WESTERN FRONT. Dispatch Riders at the end of their journey (near the trenches) resting. Battle of Messines Ridge.']
digital.nls.uk/74547060