How to work with my image with the color picker

Are you trying to use Menucool color picker to select a color from an image? No.
It is not able to do that.
It is only able to choose a color from its popup color pallette and pass
your chosen color value to the value of an HTML input element on your web
page.
If you want a color picker that can select a color from an image on your
screen, you need desktop color pickers such as http://colorcop.net/