I mentioned earlier that I'd modify ObSrv to be able to generate an RSS feed from any site that has images.
I didn't realize it, but it already does this.
Just key in the search words, followed by site:yourdomain.com
For example, if you want a feed of all images of the planet Saturn from Nasa.gov, just type in:
Or for a feed of all images of Antarctica from NationalGeographic.com, type in:
How cool is that?