The problem is that you've entirely missed the point. The code solves the problem. We don't care about recreating grayscale to match human perception, or whatever, we care about solving the answer placed in front of us.
The Sobel operation is at most 4 nested loops (really only 3) for a total of ~7 lines of code, depending on how you like your white space.
Fold the summation into your Sobel function without requiring another line.
The most complicated thing used from the OpenCV library (which I'm well aware is C++!) is JPEG decoding. OK, I'm avoiding swirling, but then it isn't needed to solve the CAPTCHA anyway.
Well put. The title is indeed completely factual! Including '23 lines' was just to let people know at first glance that the solution is simple.
> If you had to write the un-swirling, gray-scaling, Sobel filtering and summation code in Python you'd be looking at a much larger pile-o-code
I would also like to point out these are also all very simple operations, which would only take a few lines of Python/C/whatever to do. Python just happens to have a pre-written libraries to save reinventing the wheel.