You use the same code for rewrite that you normally use in .htaccess but since putting it in htaccess in Plesk breaks any cgi script or redirects you have running on the server or in htaccess so then you will need to edit the domain's own httpd conf which is normally located in
/home/httpd/vhosts/yourdomain.com)/conf/httpd.include
and add this between the <VirtualHost your_server_ip:80> and </VirtualHost>
RewriteEngine on
RewriteCond %{HTTP_REFERER} !^$
RewriteCond %{HTTP_REFERER} !^
http://(www\.)?yourdomain.com(/)?.*$ [NC]
RewriteRule .*\.(gif|jpe?g|png|bmp)$ [F,NC]
You change "yourdomain.com" to the actual domainname you are trying to add hotlink preventation on.
And also you can add more of those per line
RewriteCond %{HTTP_REFERER} !^
http://(www\.)?otherdomain.com(/)?.*$ [NC]
For each domain outside of your domain to allow them to hotlink your images so if you have people using your banner on thier site you need to add them to the RewriteCond. Change otherdomain.com to the actual domain you want to allow hotlinking to your server images ..
Restart httpd and you should be set ..
Bill