I found myself today with the desire to incorporate a bit of watermark-ish text and graphic into a LaTeX document. The regular graphics commands don’t work very well with this, so I went googling and found the code below.
Note that the following isn’t my tip, but the page that references the code points to a 404 link. I tracked down the google cache to get the original link back out and thought I’d share.
\makeatletter \AddToShipoutPicture* \makeatothe
There are two makebox lines present. Uncomment the first to use a text or stamp the output of another command on the page; or use the second (replace the filename) to use a graphical watermark. Also, remove the asterisk from the opening AddToShipoutPicture command to have your image stamped on every page, rather than just the first.