Raimey: I think the phrase "nach ein Gemaelde von Frau Alice ..." is meant to say that the pose of Otto and his dog in the photo was set up to follow or mimic the poses in a painting previously made by Frau Alice. It's the kind of thing one will sometimes see in an art gallery or museum where a piece of art is, e.g., "after an ancient sculpture from [insert]" or "after the original in the [name of museum]", and done by a contemporary artist. Chances are Frau Alice didn't take the photo - she was a painter - and may have been long dead before the photo was taken.
Chances are, someone saw the painting and then saw Otto and his dog and said "I saw a great painting of a man and his hunting dog, and it could have been you and your dog. We could make a nice portrait, posing you and your dog like that."
I haven't been able to find anything on Frau Alice googling her name, but that could be a function of some misspelling inserted somewhere along the line or her having been [relatively] unknown as an artist.
