Optical Illusion Stroller

Here is an optical illusion that might twist your view on the world. Below we have a stroller that has the three left most wheels on the ground then cleverly the right most wheel group is off of the ground and the shadow for that wheel group is out of place.

Thomas Michael Corcoran
Used w/permission
Copyright 2004

How was this effect created? Was this done with 3-d modeling software. Was it just manipulated in an image processing program like Photoshop? Or could this be some freak of nature, a place where physics is warped and the universe doesn't play by the rules.

Let me know what you think.