Fig. 1. Imaging process of real face and photo face

Fig. 2. Comparison of real face, photo face, and their HOG. (a) real face, (b) gradient image of (a), (c) HOG of (b), (d) photo face, (e) gradient image of (d), and (f) HOG of (e)

Fig. 3. Schematic of HOG feature extraction

Fig. 4. Block diagram of HOG feature extraction

Fig. 5. Reference feature distributions of average features of (a) real face and (b) photo face

Fig. 6. Similarity distributions between samples and reference features. Similarity distributions of 1000 samples to (a) HT-mean and (b) HF-mean

Fig. 7. Block diagram of human face liveness detection

Fig. 8. Example of error samples