I have been thinking that Craig was likely correct with his Peugeot Bebe guess. However, after studying grob's very welcome close-up, I have convinced myself that the mystery car is more likely a: Wanderer W2 Model N (two seats side by side, rather than the Model H with two seats in tandem) "Puppchen" from 1913/1914. Both the Bebe and the Puppchen arise from a design by Ettore Bugatti, and hence are similar in size and appearance. But, after examining grob's enlargement, the windshield detail and hood/cowl interface lead me to believe this is a Wanderer. Also, it seems to me that a Wanderer would be more likely to have been seen in Germany in 1919 than a Peugeot.
Of course this is only speculation, as I have no proof, but perhaps my comments will provoke further fruitful thought, just like grob's enlargement did for me.