Stereograms are images hidden behind other images. All you have to do is to stare at the image and suddenly, the hidden image appears. There are a lot of site that explain how to look at these Stereogramsbecause it is quite difficult to catch the idea and to discover the hidden message beneath. Not everyone can do this from the beginning but with some practice, you will find yourself very lucky to see something that is not revealed from the beginning. It
is said that in order to view the 3D images, simply stare at the picture until the image starts to take shape. There are more ways to see the hidden image stereograms but this always works: try to observe the image like you would want to see through the visual, somewhere far behind the image. First you will see the image becoming blurry and then the image will grow and the 3D image starts to appear. I found a gallery on Eye tricks here with a lot of images and explanations that might help and also books that you can have. 3D Stereograms are beautiful images in their-self, amazing ans sophisticated visuals. Some stereograms in hi-definition here. Images from here.