However, you don't need to understand the theory of these algorithms in order to use them as shown in this book. Thanks to the OpenCV team and Philipp Wagner's libfacerec contribution, OpenCV v2.4.1 provided cv::Algorithm as a simple and generic method to perform face recognition using one of several different algorithms (even selectable at runtime) without necessarily understanding how they are implemented. You can find the available algorithms in your version of OpenCV by
using the Algorithm::getList() function, such as with this code: