How do I display a photo when no ads are served

I only started my google ads about a month ago and some of my webpages still don't display all the ads. Most webpages have ads in three places:

1) Ad unit in top right corner - these almost always display fine
2) Link unit on left hand side - display on some of the pages, sometimes only one or two links display
3) Ad unit on right hand side - display on some of the pages

This page should have ads in all 3: http://www.snowcommunity.com/whistler/index.php

This page should only have ads in the top right: http://www.snowcommunity.com/index.php

What I would like to do is be able to put an image in place of the ads if no ads appear. Is this possible? How do I do it?

Is there a way to get the ads to display in all three places on all the webpages?

Thanks

 

Thanks, got it working...

 

thanks sawn I been looking for that but have not had the time to read up on it.