This app is based on Bates method: http://en.wikipedia.org/wiki/Bates_method
3D image is a special plan in which contains implied image, by coincidence, and the separation of the eye vision, people can see the implied image.
The correct way to view:
Imagine the picture is very far away, relax the eye, consciously expand the field of view, try effort to let details become clear. You will see part of the bulge to form an image. This is the right approach, and we usually use this approach to see distant. This method can also relieve myopia, since myopia used to see near things.