No, not painted. Not a decal. It's simply a "special effects" thing, done digitally on the computer to evaluate the concept.
I took a shot of my car, and the flag, and manipulated the flags perspective and rotation to match that of the "plane" of the rear fascia. Then masked the area and inserted the flag, allowing the underlying luminance to remain so that it would contour and shaddow like it was really there.
I wish it were real, like a giant static-cling piece that I could apply and remove whenever I wanted. Now wouldn't that be cool.
Take Care, Drive Safely!