How can you see the 3D effect...
While starring at the middle of the two images cross your eyes. If you can't cross your eyes (looking down at your nose to try to cross your eyes won't work) you can't see the effect.
Simple instructions: Cross your eyes, relax your vision until there are three images, then focus on the center image. The further back you are from the screen, easier it becomes.
To better results, click on the image to enlarge and only see the image on screen.