Introduction to Haar Cascades

Before we jump into understanding what Haar Cascades are, let's try to understand how we would go about detecting faces. The brute-force method would be to have a window or a block that will slide over the input image, detecting whether there is a face present in that region or not. Detecting whether the block is a face or not can be done by comparing it with some sample face image. Let's see what the issue is with this approach.

The following is a picture of a group of people:

Figure 5.1: Picture of a group of people

Notice the variety of faces in this image. Now, let's look at the following self-explanatory representation of the brute-force method for face detection:

Figure 5.2: Brute-force method for face detection

Here, we can see how difficult it would be if we were to create one standard face that can be used as a reference face to check whether a region in an image has a face or...