how to evenly black out faces?

im trying to black out my friends face in this photo where it doesn't just look a straight black color.. can anyone help? http://ift.tt/1W9JyuE here is the picture for reference

Great design resource

100 Things Every Designer Needs to Know About People (Voices That Matter) Submitted April 05, 2016 at 04:32PM by xXK4ND3NXx http://ift.tt/1RWo4hU