Robert,
I'm not sure what "depthography" is, but I think what you are refering
to is called a Random Dot Stereogram, or RDS. These are the posters that look
like spattered paint, but if stared at long enough, a 3D image will appear. The
cool part is that you can do this yourself… even with 3DS images! (I've done
it myself!) There are several RDS generator shareware programs along with many
images over in the Graphics developers forum, in the (appropriatly enough) 3D /
RDS sections. Kai's power tools Photoshop capatable plug-ins also can make
these. All you need is a greyscale image with the light areas being the front
and the darker areas receding into the background, and the program will spit
out an RDS. In the end, they don't really have a practical use, but it's
kinda fun to make them and show them to people who just end up saying "I don't
get it, I don't see anything." <g>
David