There were enormous numbers of paintings of Hitler during the Third Reich. The annual Greater German Art Exhibition in Munich generally had several. This one comes from the 1937 exhibition, and is the work of Heinrich Knirr (another of whose Hitler oil paintings is also on the GPA. It comes from Die Kunst im Dritten Reich, the glossy art magazine published by the Nazi Party.
This and other art pieces depicting Hitler are available on the Hitler portraits page.