Blending Image in a Signature

First get your background and everything done:

Now get the stock or image that you want to use. Try to get one that has close color scheme to your background. Then Put it where ever you want:

Now set the blending of the stock or the image to Luminosity:

Ugly? I know just wait and see ;). Now duplicate the stock or the image and then set duplicate to Normal and put its Opacity to 60% (depends on the background:

Starting to look good right? Now duplicate the stock or the image one last time and set it to Screen or Overlay which ever looks nicer and make sure the Opacity is 100% (Also depending on your background):

Wallah! and you are done with a nice blended stock or image with your background.