The two dimensional representations of 3d drawings, the kind computers make these days, are so amazing for a different reason: they are precisely shaped, with realistic lighting, reflection, perspective and texture that convince the eye. For these qualities they seem at first glance as convincible and as real and three-dimensional as a real photograph

But, beginners who are learning computer graphics often like to take a challenge where they paint in a 3d drawing into a real photograph, say, a computer-drawn hat on the head of a man in a photograph, only to pass their handiwork around and ask people to find out if the hat is real or artificial. You would be surprised how many people get it wrong. The object doesn’t match up in texture and lighting with the person in the photograph.