We previously familiarized ourselves with the concepts of object detection and object recognition, but we never combined them to develop an app that can do both end-to-end. For the final chapter in this book, we will do exactly that.

The goal of this chapter is to develop an app that combines both face detection and face recognition, with a focus on recognizing emotional expressions in the detected face.

For this, we will touch upon two other classic algorithms that come bundled with OpenCV: Haar Cascade Classifiers and multi-layer peceptrons (MLPs). While the former can be used to rapidly detect (or locate, answering the question: where?) objects of various sizes and orientations in an image, the latter can be used to recognize them (or identify, answering the question: what?).

The end goal of the app will be to detect your own face in each captured frame of a webcam live stream and label your emotional expression. To make this task feasible...