Image linking is the practice of placing an <img> tag on one
site which refers to  a file on another site, thus using their
bandwidth.  This is a good thing if you post on Fark or ebay
sales or craigslist.  This is a bad thing if someone else does
these things with your images, movies, etc, and you pay the bill.
Keep an eye on your access logs, and pay particular attention
to the http_referrer.  This is made much simpiler with
AccessWatch or Webalizer.  Once you know the offending source
link, there is a simple fix.

In your <VirtualHost> directive, add this:

########
SetEnvIfNoCase Referer "^http://www.troutman.org/" local_ref=1
SetEnvIfNoCase Referer "^http://troutman.org/" local_ref=1

<FilesMatch ".(gif|jpg|png|jpeg|mpg|mpeg|wmv|avi|wav|mp3)">
    Order Allow,Deny
    Allow from env=local_ref
</FilesMatch>
########

...of course, change troutman.org to your server name or any
dervations of it.  This particular entry does not have an 
Allow from all statement, which means only local references
will be allowed, and all others dropped.

How specifically to stop a malicious linker?  Say you wanted
to allow any image linking except ebay:

########
SetEnvIfNoCase Referer "^http://www.ebay.com" ebay=1

<FilesMatch ".(gif|jpg|png|jpeg|mpg|mpeg|wmv|avi|wav|mp3)">
    Order Deny,Allow
    Deny from env=ebay
    Allow from all
</FilesMatch>
########