Palm Print Image preprocessing

Dear All, 
          i am having a problem in palm print image preprocessing. Actually, i want to determine the turn points between the fingers. For this, first i m converting gray scale image into binary image and then   determine the boundary pixel of hand. Among these boundary pixel how can i determine the pixel value between the fingers. I m trying a lot to determine the curve among the boundary pixel but i did not get success. Can u please suggest me anything regarding this. I'll be very thankful to you.