The item can be found in the far left-hand end of the building where you cook the sausages. In order to gain access to the building, you'll have to fill the dog's water bowl at the order of a soldier.
"Even though photography was not widespread, many soldiers had their photos taken before setting out for the war. Professional prints were developed on photo paper and applied to a hard backing to prevent tearing. Some photos were directly printed as postcards, especially group conscript photos."