If are you dealing with frontal faces, It would be solved simply.
Thus, You can solve that problem using face symmetry feature.
After localizing the eyes and aligning the face, divide the face two parts-left one and right one.
Then scanning line one by one, at first, search the image part where intensity gradient change fast and check whether the part exists in two facial parts equally.
If are you dealing with frontal faces, It would be solved simply.
Thus, You can solve that problem using face symmetry feature.
After localizing the eyes and aligning the face, divide the face two parts-left one and right one.
Then scanning line one by one, at first, search the image part where intensity gradient change fast and check whether the part exists in two facial parts equally.
If it's not, then the part is occlusion.