How to determine the size of a face in pixels from an image

I am given an image to load onto matlab. I have to determine the size of each face in the image in terms of pixels (i.e 48x48 pixels). Without using any matlab toolboxs, how could I find the size of the face?

Sample image

[KSSV]

You have to attach one image to help you on.

Answer 1

[Image Analyst]

Maybe try drawpolygon to trace the face. Then get the x,y coordinates of what you drew and call polyarea.