At first glance, the winter landscape seems remarkably straightforward. Snow covers the ground, tall trees stretch upward through the scene, and a deer immediately becomes one of the easiest objects to recognize. Nothing appears especially unusual, so the viewer may quickly decide that the picture contains exactly what it seems to contain. Yet the puzzle asks for something else: somewhere within the arrangement of trunks, branches, shadows and open spaces is the suggestion of a human face.
The challenge is not necessarily that the relevant shapes are invisible. Instead, they
