The Hollow-Face Illusion is an optical illusion that appears to show a hollow face when viewed from certain angles. It is created by a flat, two-dimensional image that appears to be a three-dimensional face when viewed from certain angles. The illusion is created by the way the light reflects
From Wikipedia
The Hollow-Face illusion is an optical illusion in which the perception of a concave mask of a face appears as a normal convex face.