Create a Photorealistic Car Render using 3DS Max and Vray

http://cg.tutsplus.com/tutorials/autodesk-3d-studio-max/create-a-photorealistic-car-render-using-3ds-max-and-vray/

Apply Decals using a Composite Map

http://www.cgrats.com/apply-decals-using-a-composite-map.html