From Wikipedia

Hitler's Museum
Part Two

On 21 June 1939, Hitler set up the Sonderauftrag Linz (Special Commission: Linz) in Dresden and appointed Dr Hans Posse, director of the Gemäldegalerie Alte Meister (Dresden picture gallery), as special envoy. The Sonderauftrag collected art for the Führermuseum, which Hitler wanted to build in Linz, his hometown in Upper Austria, and for other museums in the German Reich, especially in the eastern territories. The artworks would have been distributed to these museums after the war.

The Sonderauftrag was located in Dresden and consisted of art historians in service of the Dresden Gallery of Paintings, e.g. Robert Oertel and Gottfried Reimer. Posse died in December 1942 of cancer. In March 1943, Hermann Voss, an art historian and director of the Wiesbaden Gallery took over the Sonderauftrag Linz.

The methods of acquisition ranged from confiscation to purchase and includes many cases of forced sale, using funds from sales of Hitler's book Mein Kampf and stamps showing his portrait. The purchases were mostly stored in the Führerbau (Hitler's office building) in Munich; the confiscated artworks were stored in deposits in Upper Austria. Since February 1944, the art works were moved to the salt mines of Altaussee to protect them from increased bombing. Detailed records of the collection were kept at Dresden and moved to Schloß Weesenstein at the end of the war, where they were confiscated by the Russians.