How do they bead prom dresses?

It looks like a million beads are randomly scattered on a prom gown.  Did someone just sit down with the gown and randomly attach all of those beads?   No.  Not exactly.  If that was the manufacturing process, they would have no continuity of quality or design.  The beading pattern is printed on the dress.  (I'm posting a picture of a prom gown that we altered this year.)

In order to take up the bodice, I have to remove all of the beads that are in the way of my new seam.  This exposes the beading pattern. Each circle represents a bead, and has a symbol in the center of it.  The symbol is a code for which size bead should be stitched there.  Pretty nifty, huh?

After I clear the beads away, I must take up the dress and then re-bead it where it is bare along the seam.  No wonder it takes a while and costs more than casual wear alterations!