As requested here is how I make scars in textures (I used only faces in this tutorial, but it's the same process for bodies :}). This is not the best way to do it either, but it's the only way I know how to do it; my photoshop skills are pretty low lol.
this brush pack. It's made for photoshop, but if you use gimp just copy and paste the brushes into your gimp brush file. I just pick the brush I want and select 'dodge'.
http://1.bp.blogspot.com/-GnoNf0M-ekc/TmK1v6A9uJI/AAAAAAAAA_Q/4w9ADAXnEjg/s1600/ScreenShot6186.jpg It might be hard to see because I use HDR lighting and that makes everything really shiny. Below is his actual texture (will upload on request).