I have several binary images and my task is to segment circle-like shape. The circles are not perfect rounded circle, but all of them will look like circle. Here are some exampl
You can use hough transform, first you need is the edge image then you use a hough transform like you can see in this papers
http://www.cis.rit.edu/class/simg782/lectures/lecture_10/lec782_05_10.pdf
http://www.sci.utah.edu/~gerig/CS6640-F2010/FINALPROJECT/Ballard-GHT-1981.pdf
http://www.sciencedirect.com/science/article/pii/003132039290064P
http://www.markschulze.net/java/hough/
Do you know the radii of the disks you are looking for? If yes, morphological openings (erosion then dilation) would be straightforward, and very fast. The result using Mathematica:
Opening[img, DiskMatrix[15]]
If not, as other proposed, computing the contour image and then using the Hough transform would be a method worth pursuing. The image just above shows the contour image.