How to detect lines arranged in a visual pattern in an image?
If it is a true bw-image, i.e. it contains binary values only, you can use the Hough transform for circles (or a special one for ellipses). In the Hough space you will find maxima for the coordinates of the center and the radius or radii, respectively. If necessary, you can use a statistical test to proof the maxima since there are offen multiple local maxima.