Detecting circles in an image

How can i detect the circles in this image? I've read some files but the codes are too complex and hard to understand, can anyone show me how to do detect just the circles in the image in a simple way?

[IMG]http://i1122.photobucket.com/albums/l527/adamazwan/circles.jpg[/IMG]

http://i1122.photobucket.com/albums/l527/adamazwan/circles.jpg

Answer 1

[David Young]

You could try normxcorr2. There's example code in the accepted answer to this question.