Our perception of an image can be completely different than what the actual image is. Sometimes when we view something as three dimensional it is actually a flat/hollow object. Light also tends to alter how we view things and something can seem completely different just based on the presence or absence of light. This video shows an example of depth perception when viewing a window with a rod thew it and as the window turns we see that the window and rod are not positioned how they appear. The second video shows two faces one of which is hollow and the other 3D but both appear to be 3D. They are also shown in the presence of light and how it affects their appearance.