These images are called "single image stereograms,", which is a
special type of 3D image that uses one, instead of two, images as the
"raw material" for viewing three-dimensional images. Here is a link
to a good website for an explanation of the various type of 3D images:
BBC: 3D Stereograms
Here, from that website, is a rather technical definition of a "single
"6. Single Image Stereogram (SIS)
"Tyler's improvement on Dr. Julezs' Random Dot Stereogram, whereby the
two images are merged into one picture. There are several variants:
"1. Single Image Random Dot Stereogram (SIRDS6) - Consists of a single
image stereogram with a random pattern instead of a texture.
"2. Single Image Random Text Stereogram (SIRTS) ? Instead of dots,
ASCII text is used for two-dimensional image information.
"3. Single Image Texture Stereogram (SITS) ? This SIS uses texture in
place of a random pattern. There are three basic forms of SITS ? those
with internal 3D elements integrated into a 2D picture, floaters
(visible elements that appear to float in space at different depths)
and floaters integrated with a hidden 3D image."
And here is a link to an entertaining website that offers a selection
of such stereograms and links to other sources of these images:
Benlo Park: Stereogram Gallery
I found these sites with the following Google search:
focus 3d images called stereogram
If you conduct this search yourself, you will find much more
information and many examples of the "single image stereograms" that
I am confident that this is exactly the information you are seeking.
If anything is unclear, please ask for clarification before rating the