There are four non-hologram depth producing processes that have been used on stamps to date:

Anaglyphic -  where a pair of glasses are required.  Two basic types exist:  Glasses with two different colored lenses, with which one views bicolored images overlapping one another, slightly offset so that one color is viewed with one lens and the other, from a distance to the right or left of the first one, that provides parallax so that the frequency of the light causes the images to appear overlapped and deep.  Italy issued the first stamp that needed glasses with colored lenses. 

The newer types of glasses have uncolored (clear) lenses that use optical characteristics to provide parallax that gives the illusion of depth, or are a sub-type that causes eyes to focus simultaneously on two  images that are placed side by side,  but viewed on top of one another through the glasses.  The parallax is captured in the side-by-side images to give the impression of depth.  San Marino's new 200 issue (below) uses this technology.

"Cross-eyed" Viewing - No glasses are needed.  Two images are interspersed with near and far objects alternated into one complete picture.  One has to train one's eyes to focus on two images very close, so that one eye will perceive the close up image embedded in the composed graphic, and the other eye will view the farther appearing image.   Finland used this graphic technique.

Lenticular 3D - This is the  system Bhutan used on it's issues in the 1970s, where an image is graphically split into alternating strips, with every other strip capturing either the foreground or the background of the image.  A lenticular screen is applied over the stripped together picture (the screen is really a plastic overlay  that has vertical ridges that are essentially lengthy, vertical lenses).  The lenses are conceived so that th left eye sees every other strip in the image to perceive the foreground, and the right eye sees the other strips to perceive the background.  The distance of the two eyes from one another causes each eye to see either fore- or background, thus providing the parallax needed to see depth.  View a  Bhutan 3D stamp from the rear with bright light shining through it, and you'll be able to make out the strips. 

A new development out of New Zealand, using computers, can capture multiple successive images under one special form of lenticular overlay, so that when the stamp is moved, the images can be manipulated like a frame in a movie film, giving the sense of motion.  While 3D depth isn't the primary effect sought through this process, the motion provides a sense of depth.  Short lengths of actual video can be embedded in this way.  Austria, Canada, France, Australia, Switzerland and Ireland are a few of the countries that have issued stamps using this technology in the last couple of years.  The Football stamp from Austria at the upper left corner of the web pages on this website is one such stamp.  Unfortunately, the server on which this website is mounted doesn't yet allow us to show you the moving image.

To see the images move that the company Outer Aspect has produced, visit: 
 
                                                http://www.motionstamps.eu/pages/press.html

The company's ski souvenir sheet for Finland is truly spectacular!