A simple demonstration of displacement mapping on photoshop.

Creating a displacement map is best done with an additional amount of manual augmentation of the source image. Simply creating a greyscale version of the subject and applying a texture with the displacement map filter is often too subtle to have a noticeable impact. I find that manually adding shading to your source image thereby accentuating the features will do a better job of warping the texture to the map. Adjusting the levels and so on is also a necessity.