I recently read some article about parallax mapping when I got the idea that it could not be that difficult to realize that inside the Blender Compositor since the Blender internal render-engine does not support it.
Tag: Displacement
Based on this Article about Non-photorealistic Rendering Using Existing Tools (SIGGRAPH 2009), there was an interesting discussion on different Blender Forums about the different techniques to get a painted-looking result with the Blender Internal Renderer.