Filling Holes Example
From MATLAB Techniques for Image Processing by Steve Eddins.
Filling interior "holes" in binary image objects is frequently useful for cleaning up segmentations.
I = imread('coins.png');
imshow(I)

bw = im2bw(I,graythresh(I)); imshow(bw)

Fill holes using imfill.
bw2 = imfill(bw,'holes');
imshow(bw2)

Note: You can also fill holes in gray scale images using imfill.