Adding a Background or Watermark?

I have just put together a Page for our newly forming young adults & professionals small group: http://firstbaptistchurchsh.com/node/28

This is not a "singles" group as is far too common because I don't believe that they are healthy.

This is an Intake/Welcome/Invite-a-Seeker-or-Drifter ministry which may lead to a larger culturally-relevant celebration service with spin-off groups.

That context stated I'd like to put a background or a watermark on the page to make it more interesting, either a picture of our own new Holy Grounds Coffeehouse or something generic.

Is there a preferred way to do this?

Is it possible to slideshow a folder of images as the background to keep it fresh?

Thanks!