Remember that controversy last year about the Jackson Pollack paintings that were found in a closet, only to have their authenticity dismissed by a physics professor who used "fractal analysis" to prove that they were "substantially different" from real Pollack paintings? Well, it turns out that his fractals weren't that useful after all.
On a related note, I still remember a great exhibit at the Met back in 1996, which showcased paintings that were formerly attributed to Rembrandt, but were now just attributed to "the school of Rembrandt". The exhibit was a humbling lesson in connoiseurship. My eye was able to work backwards: once I knew that something was a fake Rembrandt, I was able to "see" all the subtle "flaws" in the painting. Of course, if it was a "real" Rembrandt, I just stared on in awe. Was the difference real, or only imagined? The answer seems besides the point. There is no way to quantify the sublime, no matter how precise the fractal analysis gets. Great art is like porn: it's impossible to define, but you know it when you see it.