(Berlin 1872 - Düsseldorf 1956)
German painter, woodcarver and woodblock printer.
Otto Acckermann according to the few biographical facts there are was trained at "Eschke in Berlin". This undoubtedly was naval and landscape painter Hermann Escke (1842-1900) who was awarded the title of Professor Imperial and close enough to the German Imperial House of Hohenzollern to have his son Hans Hermann appointed German Consul General of Singapore, in 1889, so that must have been by Kaiser Wilhelm II who came to power in 1888 (until 1918). Hans-Hermann Eschke became the first full time German diplomat.
Otto Ackerman however stayed closer to home and wandered from Berlin to Düsseldorf in 1897, where he was to stay the rest of his life traveling to Belgium, Italy and into the Netherlands. He painted landscapes and Belgian and Dutch coastal scenery.
Possibly Otto A. is identical with the (G or O) Ackermann of the before posting. This woodblock print by Otto Ackermann, it is the only(!) one I could find, from the van der Grinten collection depicts Kaiserswerth on the Rhine near Düsseldorf. Sadly the signature isn't visible in this photo. German colleague painter Theodor Hagen (1842-1919) painted this romantic location too, the Ferry house and Inn on the banks of the Rhine river.
And, according to this early 1900 postcard, they were both pretty acurate.