Code:
RewriteEngine On
RewriteRule ^((urllist|sitemap_).*\.(xml|txt)(\.gz)?)$ forum/vbseo_sitemap/vbseo_getsitemap.php?sitemap=$1 [L]
RewriteCond %{HTTP_REFERER} !^$
RewriteCond %{HTTP_REFERER} !^http(s)?://(www\.)?examplesite1.com [NC]
RewriteCond %{HTTP_REFERER} !^http(s)?://(www\.)?examplesite2.com [NC]
RewriteCond %{HTTP_REFERER} !^http(s)?://(www\.)?examplesite3.com [NC]
RewriteRule \.(jpg|jpeg|png|gif)$ - [NC,F,L]