If this has been discussed before, I apologize.
Quote:
The World Association for the Development of Philately (WADP) and the Universal Postal Union (UPU) jointly conceived and developed the WADP Numbering System - WNS, which was launched on 1 January 2002.
This is a quote from the home page of a website discussed in the latest Linn's. I'm not really impressed by the numbering system so much as the database of every legitimate (?) stamp produced worldwide. You can download pictures of each stamp for your personal use.

Check out the site - I think you will find it a useful addition to your favorites list.
http://wnsstamps.ch/en