It looks as though he used only two widths of paintbrushes to create the stippling effect. Very economic and resourceful.
Or maybe he only had limited tools with him at his brothers home.
Or maybe he only had limited tools with him at his brothers home.
...
I think Van Gogh either painted in the open air, in the cafe, or in his room at the asylum. I think his brother sent him money and then Van Gogh used that to buy his canvases and tools.
An example of what the software looks for in Van Gogh's work is a low number of brush strokes to create an object (probably a facial feature in a portrait).