How to view a stereograph (3D picture) with nothing but your eyes
To view a stereo pair without some sort of glasses or a special screen is relatively easy, and you have two methods to choose from: parallel viewing and cross-eyed (x-eyed) viewing. Which one is the easiest differs from person to person. One advantage of the cross-eyed viewing method is that you can view larger pictures than with the parallel viewing method. Both methods are explained below.
When looking at a stereo pair, you should look 'though' the picture, so that your left eye looks at the left picture, and your right eye looks at the right picture. When you relax your eyes, you should notice similar objects in each of the pictures moving toward each other until they overlap each other. When the pictures overlap completely, you should be aware of three pictures side by side. When your eyes get used to looking at the 'middle' one, you should see it in stereo (3D).
If it proves too difficult, it may help to put a piece of cartboard vertically between the pictures and looking with the cartboard between your eyes.
Sit in front of the stereo pair, so your nose lines up right between the two pictures. Bring your finger from the middle of the two pictures slowly toward your nose, and focus your eyes on your finger, while being aware of the picture in the background.
As your eyes begin to cross while you move your finger closer, you should notice the two pictures in the background beginning to spread apart with a third picture appearing (should be when your finger is about halfway between the picture and your face). Try to 'focus' to the middle picture, while your eyes are still crossed. When you can remove your finger, you should see the picture in 3D. Large images can be viewed using this method.
Good luck! If you're successful, have a look at the pictures for parallel view
and cross view