We applied depth perception to detect the distances between objects and ourselves. Without it, we can not even catch the coffee cup, for we are not able to know how far our arms need to stretch out to reach the cup. There are two major cues for depth perception, relative size cue and linear perception cue.
Now, look at the pictures below.
What a surprise! Our perception tricks us, assisted by the tilt shift photography and the "little coin".
The tilt shift photography applied in the pictures above is originally to promote the quality of the wide-angle picture. Just like our eyes, the camera sometimes create severe tilts of objects' outlines in a picture, which is a disaster for photographers who want to reproduce the original scence, but quiet important for us to perceive depth, known as linear perception cue. The tilt shift photography corrects these tilts by applying modification on the lens. So the objects are no longer out of shape. Simultaneously, the linear perception cue is weakened, which makes the objects look like toys.
In addition, the coin gave us a relative size cue to estimate the sizes of the objects. But in this case, it is a false positive cue intentionally made by the photographer.
The tilt shift photography is quiet popular today. There are more such photos on this website: http://www.moillusions.com/2011/06/6-cool-examples-of-tilt-shift.html.
Can you remember any other kinds of illusion photos you have seen? And how it tricks your perception?