file: OpenCV-2.3.1/samples/python/chessboard.py [[OpenCV]]-2.3.1/samples/python/chessboard.py

problem: URL is invalid

solution:
changed this: https://code.ros.org/svn/opencv/trunk/opencv/samples/c/left01.jpg
to: https://code.ros.org/svn/opencv/trunk/opencv/samples/cpp/left01.jpg

I also added a try statement which tries loading the local copy of the file, found in the same repository.