I could really use some help here. Who are these men? Which branch of the military are they from? What nation’s armed services do they serve in? The previous owner of this vintage real photo postcard stated that the men seen in this image are a group of World War 1 medics. I can not confirm his statement, but it is true, that the soldier sitting in the middle of the bottom row, has red cross patches on both of his upper sleeves. At least this man, seems to be in a medical unit. Another clue might be the observation that the gentleman, third from the left in the top row, appears to be wearing a World War 1 era uniform. Speaking of uniforms, why is it that all eight of the men wearing badges on their hats, have different badges. These men’s uniforms are certainly not uniform. I am eager to hear cabinet card gallery visitors opinions about the identity of this military group. This postcard is postally unused, has excellent clarity, and is in very good condition (see scans).
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THE CABINET CARD GALLERY 
This image would have been made at a British military convalescent hospital or Command Depot (convalescent camp), hence the different regiments represented in the cap badges. The uniforms belong to the hospital. You can find another example here https://wellcomelibrary.org/item/b18863231#?c=0&m=0&s=0&cv=2&z=-0.0208%2C0%2C1.0417%2C0.6614
Thank you so much for providing an answer to many of the questions presented by this photograph. Your comment is very appreciated.