Optical Illusion: Reassure us, you also see the circles on this image?

There are sixteen circles on this image.  You will understand that you must find them. If the exercise seems simple at first glance, it has stuck a damn migraine to Internet users. It must be said that the image shows only rectangles.

 So the big question is: are you able to see the circles? No ? Really ? You are advised to look carefully between the rectangles.