Introduced with the Vision libraries in Play Services 8.1, Face Detection makes it easy for you as a developer to analyze a video or image to locate human faces. Once you have a list of faces detected on an image, you can gather information about each face, such as orientation, likelihood of smiling, whether someone has their eyes open or closed, and specific landmarks on their face. This tutorial will teach you how to detect faces, gather information, and find specific landmarks.
Source files for the Envato Tuts+ Tutorial: An Introduction to Face Detection on Android
Read this tutorial on Envato Tuts+.