Depth Cues: Creating the Illusion of Depth - Flash 3D: Animation, Interactivity, and Games - page 20

A simple visual cue called relative size is easy to reproduce. Take a look at Figure 2.4.
The size of each object suggests its relative distance to the viewer. Objects larger in
scale are perceived to be in closer proximity than smaller scaled objects. Even though
this is a flat, two-dimensional image, the man on the left appears closer because of his
larger size when compared to other men in the scene.
Figure 2.4 Relative size—which man is closer?
Figure 2.5 Interposition—which object is closer?