I have tested the snake (active contour) algorithm from Chenyang Xu and Jerry L. Prince (<http://www.iacl.ece.jhu.edu/static/gvf/>) in order to extract feature border. It works very well.
However, I did it only on a single sample extracted from a bigger image which contains hundred features (as you can see below).
How can I repeat this process automatically to the whole image and thus, obtain the contour of every feature? For information, I already have the center coordinates for all features.