I just watched a really interesting article about drawing the human face: it focused on what made a face recognisable.
Most folk, when drawing a face, overly focus on the particular characteristics of each feature, the eyes, nose, etc. In this article, the author demonstrates by showing some old black and white photos that were lit so that there was a high contrast between light and dark on the faces. He was able to show that actually it’s more about overall shapes and proportions that the fact that someone has almond shaped blue eyes. By looking at the shapes the light and shadows make on a face, we can capture a true likeness of someone. This makes perfect sense, as rendering any 2 D form to give an impression of 3 D requires the correct use of value to convince the viewer – light and dark.
I had a rifle through my photos and pulled out one of my daughter on a sunny day, where her face had significant shadow on it. I found this approach so easy, and anyone who looks at this knows exactly who it is.