Postage stamps are generally printed in large sheet form with 400 images for small format regular issues, or 200 images for standard size commemorative issues. The sheets are cut into four “panes” of 100 or 50 images respectively, for distribution to post offices. (There are a number of exceptions to these layouts, especially among more recent issues.)
The large sheets are printed from a metal printing plate that contains a reverse image of the sheet. For stamps produced by line engraving, also called “intaglio”, the engraver begins the process by recess engraving the stamp image in reverse on a soft metal plate called a “die”.