Ponzo Illusion (Railway Lines Illusion)
The upper line looks longer but actually two horizontal lines are the exact same length.
The effect of the Ponzo illusion is often attributed to linear perspective. The upper line looks longer because we interpret the converging sides as parallel lines receding into the distance. In this context, we interpret the upper line as though it were farther away, so we see it as longer. In the three dimensional world, an object located farther away would have to be larger than a nearby object for both to produce retinal images of the same size. This explanation is often referred to as the perspective hypothesis. (New World Encyclopedia)
Additional images can be seen at: www.moillusions.com
Ponzo Illusion (Three rectangles)
Three rectangles are actually the exact same size.
Three soldiers and three cars are actually the exact same size as shown by moving the soldier, the rectangle, and the car cover on the left to the right.