Matlab Image Processing Help (Image Segmentation)

Hello,
I m a computer science student and i m working on a project on matlab and currently im stuck in a problem.The problem is that i want to

extract head from this image without using imcrop command meaning that it should automatically search and detect the head(keeping this as the

basic or common shape of the head) and extract the head from the background.Assuming the shape of the head to be like that for every image

but "the size may vary".
Here is my sample image for the head shape
#-Link-Snipped-#

I would really appreciate your help,suggestions,references and support
or a sample code/demo on a matlab would be nice