Parallax view with complex multiple layers of 2d art. If scrolling / panning left to right, the layers at the back would move slower than the ones nearer the front. In this case the setup is for a zoom through the images not a pan or scroll. You can tell this because the panels are all the same width ( see below )
A simpler depth layout. The background sky would not move at all . The foreground palm trees would pass by soonest. The foreground elements have to be longer than the back ones as when scrolling they move faster past the camera.
This is a four level depth environment I made - the front layer was even longer but I cropped it. the back layer represents the widest camera framing. When layers are moving this scene gets a real feeling of depth. This is a concept for an iPhone game app background - the scrolling backgrounds being relatively easy to program and giving a great sense of depth to the game occurring in the foreground.