Protecting your site's content
More info/resources
By Mike Slocombe for Internet Magazine, Feb 2004

BANDWIDTH THIEVES
Bandwidth theft happens when a site embeds your content on their pages by directly linking to the files on your server. If your site is hosted on an Apache server, you can use the .htaccess file to block bandwidth bandits:
.htaccess method explained

You can also use free CGI scripts to display an error image if a site tries to directly link to graphics on your server.
Ace BandWidth Protector:
Anti-leech

More info:
Protecting Your Work from Electronic Pirates
Bloody Thieves - copyright issues
Protecting your copyrights on the web
How Do I Stop People From Downloading My Graphics?