Prevent hotlinking

As the title says, how do you enable hotlink protection and redirect the requests to another image. I have it working with no problems on nginx, but OLS is another matter - and I need it as I've got some leeches steeling images (and bandwidth) from the site as they just use my images in their HTML code.

This is what I've tried:
RewriteCond %{HTTP_REFERER} !^$
RewriteCond %{HTTP_REFERER} !^http://(www\.)?twowheeldemon\.com/.*$ [NC]
RewriteRule .*\.(gif|jpe?g|png)$ https://twowheeldemon/images/hotlink-warning.jpg [R,NC,L]
but it hasn't worked.... needless to say, I've had to go back to nginx for now.
OK... to answer my own question... this works where the above would not
RewriteRule ^(.*)${REQUEST_URI} [R,L]
RewriteCond %{HTTP_REFERER} !^$
RewriteCond %{HTTP_REFERER} ! [NC]
RewriteRule \.(gif|jpg|png)$    /images/hotlink-warning.jpg   [R,NC]