title: circular objects detection
body: <p>please suggest me some algorithms for circular object detection, 
  for example a CD is placed under the book, and some part of it can be seen.
  So the algorithm should be able to detect a circle from the part of the CD.
  Or it can be a plates placed one above another and so on.
  I tried opencv's Hough transform, but it do not always detects all of the circles and even sometimes detects false circels.</p>