Sorry to bump up such an old topic but I'd like to tell my feelings about using these methods after havig them in use for some time..
here's a htaccess file for you
RewriteEngine on
RewriteCond %{HTTP_REFERER} !^$
RewriteCond %{HTTP_REFERER} !^http(s)?://(www\.)?partanen.net [NC]
RewriteRule \.(jpg|jpeg|png|gif)$ - [NC,F,L]
it doesn't show the images when another site calls them (hotlinking) but allows the request if you just copy/ paste the pic URL into your browser. If you don't like that behavior then delete RewriteCond %{HTTP_REFERER} !^$ (not recommended cause you'll block a lot of software firewall users form your site)
I used that in my .htaccess and listened to what people have to say about it.
The results were that most of firefox users had problems viewing the images (none show up) and myself had problems with Opera and IE not showing up all the pics and the proper links to files in the gallery would show a 403 error I customized for hotlinkers.
Even hitting refresh several times did not allways show all the images in the albums thumbnail/filmstrip view.
Even playing around the users firewalls did not allways have any affect. Maybe everyone configs theis kewl FF browsers to kill all the referrer info or something.
Thus removed that referrer thingamajigger from the .htaccess I used.
And no I'll just munch my carpets whilst being BW raped by people who link the pictures, not the gallery links.
Oh well, You don't allways get all you want, and sometimes You get somethings You don't want...
EDIT:
Forgot to say that the method Stramm gave me was fully functional with some side effects and I still take this case as solved.