German history museums do have a problem in how to tell the story of Hitler and his rise to power, along with the damage that was done to the country. It’s not possible to just airbrush him out of history, but they don’t really want displays that become shrines.
This is a very clever way of dealing with the problem, they’ve displayed the picture upside down. It was painted by Karl Rickelt (1857-1944) who moved to Cologne in 1936 and who was Hitler’s portrait painter. It is thought that the scratches to this artwork, which was a preparatory piece for a larger image at the city hall, were made by Rickelt’s wife.
In total he painted 29 artworks of the Fuhrer, more than any other individual. His own politics aren’t entirely clear, although it’s clear that he had sympathy for Hitler as a person. For his wife, who outlived him, she was left to deal with the reputation of what her husband had done in glorifying the German leader, so it’s no surprise perhaps that she vandalised this painting.