|This does work!
By exchanging the right and left views it is possible to obtain (with some
strain) a 3-D effect without any equipment. To view the crossed-eye view
shown here, move slightly back from your normal viewing distance and place
your viewpoint on a line perpendicular to the center of the image. Place
your finger halfway between your eyes and the image and view your finger.
The three bright spots between the pictures should become four spots, and
the two images become three. If the focus of the eyes is now allowed to
drift to the surface of the screen without uncrossing the eyes a three
dimensional depth illusion will appear in the central image. The finger
may now be removed from the view. A viewer may find that the extra side
images disappear once in-depth view of the central image is stable. This
is a popular way of presenting images on computers but it is difficult to
learn and for many viewers the method is not comfortable enough for
extended viewing. It also offers none of the advantages enumerated above
that are provided by the stereoscope.
[copied directly from
the Wikipedia article on