In POW (prisoner of war) camps, prisoners were able to make and use their own stamps and postcards in the camps with available material like carved wood and ink. In the early period of the war, the use of regular paper was limited. Some stamps were produced from cigarette paper.
POW camps were given location codes. There are four prisoners of war camps for officers (called "Offizierslager" in German, abreviated as "Oflag"):
Murnau am Staffelsee
Inter-Camp Polish Post in Germany in 1945 (www.stampdomain.com)
Prisoner of war camp
Prisoner of war
List of POW camps in Germany