Eye mapping?

This is not an eye mapping but just a simple exercise for your eyes. I've been kept this picture for so long and now I'm feel happy to put it here. For your information, this picture make me confuse everytime I look at it. Even I know the answer, but my eyes can't give a good concentrate on what I'm looking for.

What is this?
It's twelve of them at first. Suddenly, look at carefully because the number of man increases to 13. Why and how?

I knew that you also have this picture and maybe certain of you will say that this is an old trick....but, will you dare to try it at a higher stage?

It's gonna be like this:
Close one of your eyes and try to find the right picture. It's easy as that....!