useful links: http://stackoverflow.com/questions/27520991/opencv-best-way-to-detect-corners-on-chessboard http://stackoverflow.com/questions/24135289/python-opencv-detect-lines-in-a-tennis-court-using-two-differents-methods-of-h http://aishack.in/tutorials/sudoku-grabber-opencv-plot/ http://opencv-python-tutroals.readthedocs.org/en/latest/py_tutorials/py_imgproc/py_houghlines/py_houghlines.html#hough-lines http://opencvpython.blogspot.hu/2012/06/hi-this-article-is-tutorial-which-try.html