Seeing the 3D image
To see the 3D image in the stereogram on the back of my card you need to have stereo vision. Most people do so the chance of it working are high. To test if you have stereo vision, close one eye and hold a finger up infront of your face at arms length, obscuring the letters '3D' in the title above. Then open that eye and close the other one keeping your finger still. You will be able to see the 3D letters again due to what is called 'parallax' which simply means each of your eyes view an object from a different angle. Now focus on your finger. The screen behind is out of focus. Now focus on the screen. The finger infront is out of focus.

If that all worked as described then you have normal stereo vision. The image above tricks your vision into thinking that there is an object infront of a background. When you look at the screen you see a flat image with coloured bubbles all over it. The image is actually made up from two overlaid images that mimic parallax. They are almost identical but are skewed as if viewed from separate eyes. To see the '3D' image you need to get the left eye to just see the left image and the right eye to just see the right image. This used to be done in comics and films by printing red and green inks and wearing red and green filter glasses. Here the images are interlaced.

What you need to do is to 'relax' you eyes as if you were looking about 15mm behind the screen (ie. making your eyes more parallel than they are when you focus on the screen. Soon your vision will lock onto the background and then you'll start to make out a shape floating infront of it. If you see a hole in the background then you've done it the other way round and effectively crossed your eyes.
If you're still stuck, click on the image to see the shape you're looking for and then try again.

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