I never noticed that!
It's impossible to tell from the C6 pic (it's grainy) as to what those dark lines are from. It could be cammo, it could be a decal, it could be an alteration of the original picture (notice we never seem to get 1600x1280 pics, always shrunk!).
BUT, I'm certain it isn't[/b) a real shadow or indication of a realistic body-crease after comparing all of the other shadows, degrees of shadowing, and the position of the sun in the that picture.
I suppose that COULD be an old body testing car and that COULD have been a deep crease (doubtful). But, the other spy shots we have show no indication of it.