Dachau was initially a camp for political and ideological opponents of the Nazi regime, e.g., union leaders, communists, and social democrats. Jews who were members of these groups were detained, but mass arrests of Jews did not take place until Kristallnacht, five and a half years later.

This image is the full post card. The preprinted instructions indicate that

Protective prisoners may receive 1 package of underwear every month up to 10 lbs. (food, smoking materials, etc., are excluded). In addition, one letter and one postcard are permitted. Nonobservance of the rules will result in confiscation. Visitation is not permitted.

The writer, Otto Marx, was a merchant in Bavaria. He later wrote a book about his experiences in Dachau.