Displacement maps

I am having a bit of trouble with displacement mapping. I am trying to cover a very rugged cliff face with the Union jack (british flag). I am trying to get a sort of old faded spray painted on look, following the rock contours. I am looking for any sugestions on the best way to achieve this effect, and or any sites that may have a tutorial regarding displacment.

Thank you all

First take the rock you want the flag on, copy that then make a new document and paste it. Turn it to black and white, then gaussian blur it a bit.

Save this as a psd, remember where you saved it. Then dispace the flag image with this file.

After this try setting the flag layer to overlay, or darken, try a few of them see which looks better.

Maybe just turn the opacity down a bit.

http://www.photoshopcafe.com/tutorials/dispmap/dispmap.htm

This page will help you.