I currently have my home computer set up to download the Astronomy Picture of the Day every day, resize it, and put it in my background rotation automatically.
To do it, I used a combination of
DailyStrips and
ImageMagick.
Full instructions are on my web site at
http://zansstuff.com/rotatedesktop.html#apod
If you just want to display it on another web site, DailyStrips is a Perl script, and you could set it up to run as a chron job (and write a little script to rename each day's file to a constant name or modify the Perl to always output the same name), or you could modify it so that it displayed the fetched image as an output when called by a browser.