you guys are so confused.
First of all, the image is not rigged.
Second, the illusion is caused because of the shadow being 2d and the real object it is portraying is 3d. In a 2D image u cannot, i repeat, you cannot prove what is in front or what is in back unless comparative and experiences influence is used. so the brain just chooses one randomly, but biased by your brains development.
For eg, if there is a scene of two balls positioned in such a way that both appear to be the same size from the front but one is a tennis ball and the other is a basket ball. if u take a shadow picture, like the one here, you cannot tell which ball is towards the viewer and which one is farther. but if the image is colored you can tell that the tennis ball is closer because you can compare it to the experience of your life, NOT because the image can tell you that. Technically in the image the balls are same size and cannot be proven otherwise.
Thirdly, specifically to this image, look at the image if it turns clockwise at the moment then start reading some text somewhere else on the screen. Most probably the image will change direction to anti-clockwise because the act of reading requires the left side brain to work. and if you again start just looking at the image while wondering why light has colors or something else imaginative the image will again go back to clockwise. The trick is not to focus on the image but to keep it in ur field of view while thinking things. so you will see that if u think math it will go one way and imagine abt stars it will go the other way telling you which side of ur brain is active at that time more then the other.
basically to understand this stuff one needs to think out of the box. because most people dont, or rather most brains get rigged into procedures and facts of life that are not really facts the brain can be tricked buy intelligent feedback, like eating a apple and smelling a peach while eyes closed. And since no two people have had the same experience in their life so there brains have been imprinted differently and thus the diff rotations for diff people at the same time.
so if u can think out of the box then u can get the image to rotate whichever way u want.