Are they not created by super talented people, using just the basic shapes in game, same a s the people who could do photo realistic images in forza with just the shapes..
I think they just seperated the photos in multiple layers. You can see that there are no basic shapes used.
You can see for yourself, if you download them. I found only the art of lupothewolf (He also has hundreds of decals that are worth a look......and a like):