The message on the reverse is in Danish which is why the mill has been provisionally located in Denmark. This postcard is used in "Mills at war", 2019, p.40.
The painting depicted is by Georges Scott a member of the Salon des Artistes Francais.
The postmark cannot be read, but the date cannot be before 1910 as the painting depicted was created in 1910 nor after 1939 when the stamp used ceased circulation.
German military manoeuvres on Lüneburger Heide, Hanover. The windmill is unidentified. The photograph appeared in "The Evening News". This image is used in "Mills at war", 2019, p.37.