In “Emotions Revealed,” Ekman provides a graphic photo-illustration of the difference between the Duchenne smile, the real smile and the social smile. The photos A to F and the accompanying text that follows is from his book:
At first glance it might seem that the only difference between these photos is that the eyes are narrower in photo B, but if you compare A and B carefully you will see a number of differences. In B, which shows real enjoyment with a Duchenne smile, the cheeks are higher, the contour of the cheeks has changed, and the eyebrows have moved down slightly. These are all due to the action of the outer part of the muscle that orbits the eye.
When the smile is much broader, there is only one clue that distinguishes between enjoyment and non-enjoyment smiles. A broad smile, such as in photo C pushes up the cheeks, gathers the skin under the eye, narrows the eye aperture and even produces crow’s-feet wrinkles. All of this without any involvement of the muscle that orbits the eye.
In comparison photo D the eyebrow and eye coverfold (the skin between the eyelid and the eyebrow) have been pulled down by the muscle orbiting the eye. Photo D is a broad enjoyment smile, while C is a very broad non-enjoyment smile. Photo C, incidentally, is a composite photograph made by pasting D from the lower eyelids down on to the neutral photograph E.
Photo F is another composite photograph, in which the smiling lips from picture D have been pasted on to the neutral photograph E. Human beings can not produce the expression shown in photo F. It should look strange to you, and the reason it looks so strange is because when the smile is this broad it produces all the changes in the cheeks and eyes that you see in D. I made this composite illustration to underline the fact that very broad smiles change not only the lips but also the cheeks and the skin below the eyes.