Hot linking images

Yes....

You could start logging mime types and referer (sic) (using mod_log_config, %{Content-Type}i, %{Referer}i) and see which requests don't originate from your site for image content.

There are lots of ways to prevent people from hot-linking - google will list a few. But the easiest is to ensure that the user has a current session - but this requires some smarts on your webserver, and usually that the user allows cookies.

See http://wiki.apache.org/httpd/RewriteImageTheft

Hmm, try a link:yoursite.com search on google, this shows all indexed sites linking to your domain. Maybe there's an API to fetch these results so you can filter by images.