I always do photoshop work before I customize anything. I take custom pictures the area I want to work on, import them into photoshop (or compatible program) and then compare the before and after shots.
I currently in the process of trying to get a tweeked version of the "challenger R/T" badge on my deck spoiler but don't really like the full size versions I've seen. I wanted more of the retro look thus I headed to photoshop to see if what I wanted would look ok
Here is what I did (note that these images where resized for your viewing and downloading pleasure

. They look better full size with out any image compression).
I took a picture of the rear deck in good lighting head on (as close to 90 degrees as I would)
Before shots:
I then created the asset I needed to work with, in this case the Challenger R/T badge
After overlaying, scaling and blending the two I got
Photo shop will also let you create an outlined drawing of your car if you're looking to do a whole new paint scheme.
Here is something I did really quick with an angle I already had
To get the desired look I did the following (using photoshop CS5 but these tools should be in any modern version):
- take a picture of the car with the desired angle in mind. (hint - try to take a picture without a lot of reflection as this will make it easier to clean up as you can see I used a photo I already had for this post)
- Cutout the car from the background. Photoshop and other programs have great and easy to use tools, take your time
- duplicate the layer
- from the menu - Stylize -> Glowing Edges (adjust the edges to thin lines)
- from the menu - images -> Adjustment -> invert
- from the menu - images -> Adjustment -> Black & White
- Clean up with small to large eraser tool (to get rid of any unwanted reflection lines)
Hope this helps
PS if anyone wants to see the full size image of the deck lid click
here (just under 400K)