Size Differences: As you can notice there is a row of columns in this architectural structure. As indicated by the arrows, these columns are decreasing in size to assume the appearance of a three dimensional visual experience. You can notice the specific size difference also when comparing the two highlighted columns. Because of this size difference it appears the columns are further and further away from us; however, in reality these columns are simply on a two dimensional field and are not becoming more distant.
Atmospheric Perspective: Here in this image one can make a comparison with the details on each side of the double sided arrow. In reality, our eyes view things at a distance with less clarity because light reflecting off specific objects are traveling further than off objects that are closer to us. Therefore closer object are much more clear to us. This notion is also used to presume a three dimensional aspect to computer graphics. Compare the wallpaper to the building out the window. These two are actually the same distance because they are on a two dimensional field yet because the wallpaper is much more clear than the building, it give a visual depth to the image.
Occlusion: Here in this image the hover bike is occluding all other aspects in the image. If you notice also the flag is "in front" of the boulder, which is then "in front" of the landscape. In fact none of these aspects are truly in front of each other. Our visual systems relate this image to our own three dimensional existence where objects that are close to us are actually in front of other objects that are further from us. Here in this two dimensional image nothing is really in front of anything, it simply appears that way with graphical editing to give this two dimensional image a three dimensional look.
Linear Perspective: Have you ever stood in the middle of railroad lines. If you have, you noticed the parallel lines of the railroad are also parallel to our line of vision. Therefore the railroad seems to become more narrow. This is a visual aspect that computer graphical engineers use to portray a three dimensional image. In this image there is a railroad that seems to do just what a railroad does in the three dimensional existence. To show you that your mind has simply been fooled. Those two red bars are actually identical in size and shape, and one is just placed slightly above the other. This is to show you what you are actually viewing is two dimensional, tho it appears three dimensional.
Texture Density: In this image the wooden floor texture becomes more dense as it appears to become further away. Because this is a two dimensional field the floor is simply being squished together to give it the more dense appeal. This visual aspect gives a depth sense the appears very realistic.
Lighting and Shading: In this image the snow mound is coming up from the ground. The bright lighting on the one side with the shadowing effect on the other helps to give the viewer a three dimensional feel. This progressiveness of the shadow allows for the mound to appear as a spacial object with enough height to block light, therefore producing a shadow. This effect give a realistic depth visual.