Hotlink Protection doesn't work?

Trying to implement hotlink protection on a domain that I suspect is having images “stolen”. Made the necessary entries in interworx, but hotlinking still works (tried from multiple browsers to make sure it wasn’t cached as well as online test sites).

From my .htaccess file (actual domain replaced):

# BEGIN IWORX hotlink
RewriteEngine on
RewriteCond %{HTTP_REFERER} !^ [NC]
RewriteCond %{HTTP_REFERER} !^ [NC]
RewriteCond %{HTTP_REFERER} !^$ [NC]
RewriteRule .*\.(jpg|jpeg|png|gif)$ - [F]
# END IWORX hotlink

Any ideas?

Try this block:

RewriteEngine on
RewriteCond %{HTTP_REFERER} !^http(s)?://(www\.)?domain.tld [NC]
RewriteRule \.(jpg|jpeg|png|gif)$ - [NC,F,L]