Draw OpenCV processed image within selected mouse rectangle. Alternates drawing with different image processing functions: Threshold, GaussianBlur, MedianBlur.
Demonstrates: Python classes, OpenCV, events, Window processing, File I/O, timing, and exception handling.
Python Versions: Tested with Python versions: 2.7.14 and 3.7.4
pylint: Run pylint with flag --extension-pkg-whitelist=cv2
