OpenCV versions

Closely related to using Python 3 is using a more recent version of OpenCV. This may perform better but, at the time of writing, it is quite long-winded to install for Python 2.7. It installs easily in Python 3 by using a PiWheel (prebuilt packages for Python on the Raspberry Pi).

I'll assume that pip3 is the Python 3 pip installer:

$ sudo pip3 install picamera[array] numpy opencv-python

Following this, only one OpenCV function appears to have changed enough to require our code to change.

Find contours

In OpenCV 2.4.9 this function has the signature (arrangement of parameters and return values) of:

contours, hierarchy = cv.findContours(image, mode, method[, contours[, hierarchy[, offset]]] ).

We copy the...