Partial Face Detection for Continuous Authentication
  In this paper, a part-based technique for real time detection of users' faces on mobile devices is proposed. This method is specifically designed for detecting partially cropped and occluded faces captured using a smartphone's front-facing camera for continuous authentication. The key idea is to detect facial segments in the frame and cluster the results to obtain the region which is most likely to contain a face. Extensive experimentation on a mobile dataset of 50 users shows that our method performs better than many state-of-the-art face detection methods in terms of accuracy and processing speed. 
Upal Mahbub, Vishal M. Patel, Deepak Chandra, Brandon Barbello, Rama   Chellappa
cs.CV