as someone who does these processing sessions i would say that i personally prefer sketches, done by hand.. rather than photoshop creations/modifications
many examples show that its really hard at times to tell what the final vehicle will look like in a photoshop or google sketchup or even a 3D rendering.. and that when asked for a different image and we get back a simple sketch.. its a lot easier to determine what the final vehicle will look like
my opinion: provide a sketch of your best estimation of what you think the final vehicle will look like.. show all the important angles the DMV might need to see depending on the particulars of your mutation
it doesnt have to be great! but for me personally.. a sketch tends towards being easier to figure out the intent.
ideal scenerio as i can see it?
include a sketch, or sketches, of your idea of the final vehicles appearance, detail all the stuff you plan to do and will be doing to the vehicle in the mutant vehicles mutation section of the app.. and if you feel like doing some photoshop mockups of the former vehicle post some on a website, like flickr, or another free photo sharing site, or yer own website.. and include that link in the application.