This chapter introduces some of OpenCV's tracking functionality, along with the data files that define particular types of trackable objects. Specifically, we look at Haar cascade classifiers, which analyze contrast between adjacent image regions to determine whether or not a given image or subimage matches a known type. We consider how to combine multiple Haar cascade classifiers in a hierarchy, such that one classifier identifies a parent region (for our purposes, a face) and other classifiers identify child regions (eyes, nose, and mouth).

We also take a detour into the humble but important subject of rectangles. By drawing, copying, and resizing rectangular image regions, we can perform simple manipulations on image regions that we are tracking.

By the end of this chapter, we will integrate face tracking and rectangle manipulations into Cameo. Finally, we'll have some face-to-face interaction!