http://www.learnopencv.com
https://mp.weixin.qq.com/s?__biz=MzI1NTE4NTUwOQ==&mid=2650324652&idx=1&sn=229a7f0498aca9c03409bb537ec66929&scene=1&srcid=0506O9nMeMeRjCyx6Qxdf6Ob&pass_ticket=E%2BsYGj7W6kxM%2B3DWf7E7Mac%2F3DXuOpwECGQAm%2FCrUK0%3D#rd
http://cmusatyalab.github.io/openface/
http://www.cvrobot.net/latest-progress-in-face-detection-2015/