Checking the source (referrer) of image requests

To limit access to images on your server, create an .htaccess file into which you need to place the following contents:

ErrorDocument 403 "Access denied
setenvifnocase referer ^http://(www.){0,1}domain.xyz/.* ok
order deny,allow
deny from all
allow from env=ok
v=local_ref

You can also use mod_rewrite. Example .htaccess directives:

RewriteEngine on
RewriteCond %{HTTP_REFERER} !^http://(www.)?domaine.xyz/.*$ [NC]
RewriteCond %{HTTP_REFERER} !^-?$ [NC]
RewriteCond %{HTTP_REFERER} !^http://babelfish.altavista.com/ [NC]
RewriteCond %{HTTP_REFERER} !^http://translate.google.com/ [NC]
RewriteRule .*.(jpg|jpeg|gif|png|bmp)$ - [F,L]