Using OpenCV to perform face detection

With cv2.CascadeClassifier, it makes little difference whether we perform face detection on a still image or a video feed. The latter is just a sequential version of the former: face detection on a video is simply face detection applied to each frame. Naturally, with more advanced techniques, it would be possible to track a detected face continuously across multiple frames and determine that the face is the same one in each frame. However, it is good to know that a basic sequential approach also works.

Let's go ahead and detect some faces.

Performing face detection on a still image

The first and most basic way to perform face detection is to load an image and detect faces in it. To make the result visually meaningful, we will draw rectangles around faces in the original image. Remembering that the face detector is designed for upright, frontal faces, we will use an image of a row of people, specifically woodcutters, standing shoulder to shoulder...