How to drag and adjust the face of image in a face type layout over it and get Bitmap of that particular face Area to use it in another Image view

I am making an App in android that capture the image using device camera and then drag and adjust the human face in image with the face like layout over it .Now i want to get that face area of the image in bitmap so that i can mask it with another image.
I have successfully done with image capturing but facing problem to get the human face area according to mention above .Please Guide me which is the best way to do so