you're talking about 3D pictures or stereo pictures. this one's
not one of them, coz it doesn't contain any 'hidden' picture. for
it to work, the same pattern must appear at least twice
horizontally. if you look carefully at this picture, the pattern
doesn't really repeat.
there are a few types of 3D pictures. one of them is generated by
computers, another type are 3D photos taken by stereo
cameras.
the computer generated type looks like repeated pattern, and works
by incorporating two pictures into one. they are the same picture
with a very slight variation in perspective, so that one of them is
meant to be picked up by each of your eyes. these are easier to
see, becoz the two pictures are just closely laid over each other.
the method to see these is to focus slightly beyond the surface of
the picture. they only work with very simple outlines, and don't
show complicated textures or colors, but there are programs that
convert any simple graphics into 3D pictures.
3D photos on the other hand, are two photos lined side by side.
they are the same shot taken with a slight angular difference.
there are two methods to see these. you can either force your
pupils together (which strains your eyes alot) and superimpose them
in your vision, or to use a special lens that helps to seperate
your left eye's vision from the right.
