RewriteEngine on
RewriteCond %{HTTP_REFERER} !^http(s)?://(www\.)?birincidomain.com [NC]
RewriteCond %{HTTP_REFERER} !^http(s)?://(www\.)?ikincidomain.com [NC]
RewriteCond %{HTTP_REFERER} !^http(s)?://(www\.)?ucuncudomain.com [NC]
RewriteRule \.(dosyauzantı1|dosyauzantı2|....|...|)$ http://www.siteadresi.com/yasakresimgoster.jpg [NC,R,L]