In the previous chapter, we looked at some very sophisticated algorithms used for object detection. In this chapter, we plan to look further into a different set of algorithms, known as cascade classifiers and HOG descriptors. These algorithms are widely used to detect human expressions and find application in surveillance systems, face recognition systems, and other simple biometric systems. Face detection was one of the first applications of cascade classifiers (Haar-cascade classifier) and from then on, there have been many different applications that have been developed.

Have you ever wondered how cameras detect smiling faces in an image and click a picture automatically? It is no rocket science. This chapter will talk about the different ways of detecting human expressions, using which you can build your own version of the aforementioned applications on an Android platform.

We will take a look at the following...