Image 6 - Depth 

This image conveys the sense of depth with the use of perspective and a vanishing point.  This means that objects that continue on in a straight line will seem to converge at a single point, which is one the horizon in a one point perspective.  It's a clever trick that has been used in drawing for centuries that helps fool the viewer in to thinking that the lines are receding back in to space.  

In this image not only does the footing of the brigde become narrower as it reaches the vanishing point, but the railing appears to be getting closer to each other, and the slats of the railing get closer and closer together until it is impossible to see through them. 

Also there is depth being created though size of foreground images as opposed to background images. If one looks at the post nearest to the left bottom hand corner, and compares its size in the frame to the size of one of the buildings in the background.  It is easy to tell that what is in the background is far back there, if you know the relative size of each of these things.  The mind then makes a judgment on how far you actually are.