Quote - Posing tip: No one is perfectly symmetrical. Rarely do we stand, sit, lie, squat or maintain any other pose symmetrically either. Also, the line between the eyeball and the skin around the eyes is often a giveaway to the 3D origin of an image. Usually it sharp in an unnatural way.

Those are two great points that bear repeating.

For asymmetry I always throw a random one or two in when I'm morphing (one mandible higher than the other, one cheek crease deeper than the other, nose tip a slightly crooked, etc.) - if you work off of photo references you don't have to worry about it since it's already there in the reference image.

I can still tell nearly 100% of the time whether an image is of a real person or a digital one by the eyes alone - the eyelids are very telling indeed.