This is a painting of Charles Christian Nahl from 1867. The painter hailed from the German town of Kassel and visited the local art school, before he moved to Paris and later (1867) emigrated to California.
More information about the artist can be found here: https://en.wikipedia.org/wiki/Charles_Christian_Nahl
What´s fascinating about this painting ist the early depiction of two very similar canine coat patterns in a piece of art. On the left, there is a dog with an obvious harlequin merle pattern on a brindle color base and blue eyes. It´s difficult to tell if it is Great Dane harlequin or Mh (maybe even a merle mosaic). The dog´s breed is difficult to classify as well. Louisiana Catahoula Leopard Dogs might have existed at that point of time – but the question is, if they have been around Sacramento by then. Maybe the artist has brought a harlequin Great Dane from Germany, and the depicted dog was one of it´s descendants? The dog on the right reminds strongly of a Dalmatian, with the big dots typical for the breed. These two patterns have always been – and still are – confused, but rely on completely different genetic bases (see my “harlequin” chart).