Painting by Kieran Brent Emphasis is used to highlight the person's face, because it is blurred against the regular pallor of the persons skin. This gives a visualization of what a migraine would look like.
Drawing Portraits - untitled conte on paper x cm 2013 by KwangHo Shin, via Behance Discover The Secrets Of Drawing Realistic Pencil Portraits.Let Me Show You How You Too Can Draw Realistic Pencil Portraits With My Truly Step-by-Step Guide.
This is using the Gestalt principle where we are using positive and negative space. The negative space of the coffee cup is actually a person talking and the top of the coffee cup comes out to be a thought bubble.