Kurtz's paintings

The first painting we see is identified as the work of Kurtz, the pale woman turned to the right, wearing a black dress--did anyone notice that is looks just like "Portrait of Madame X" by John Singer Sargent?

Is this just a coincidence or some sort of homage? If it is supposed to allude to something, I am not quite sure what it's supposed to mean in the context of "Heart of Darkness". Anyone shed some light?