The hybrid picture above is a well known optical illusion. It is both a picture of Albert Einstein and Marilyn Monroe depending on how far away the viewer stands from the picture. You can try it yourself: if you get back from your screen for a moment, you will see Marilyn Monroe slowly emerging.
When looking at a person from about fifteen feet, the face is still recognisable but details like eyebrow hairs, wrinkles and small moles are much less visible. This is why the photograph looks like a youngish Marilyn Monroe at a distance – we see no wrinkles or blemishes. Close up, we see various lines denoting Einstein’s eyebrows, nose and moustache and wrinkles, especially about the eyes.
It illustrates pretty well what we were taught at art school: stand back and capture the tout ensemble and do not paint piecemeal. We see things differently depending on our distance from them. To work well a portrait must be a recognisable likeness when the viewer observes it at a distance e.g. when he walks into a room and sees it on the wall opposite.
Most of my sitters do want to look their age but do not need a likeness as accurate as topographical survey. Older sitters appreciate the fact that at about fifteen feet (which is the distance I normally paint them from) I can not see very clearly the ravages that time has wrought. Unfortunately, when I do take a few step back, my models rarely turn into Hollywood stars, but then again they hardly ever come in looking like eminent physicists.