It's easy to block *everyone*, the complication (for me) is that there's a lot of people that I am happy to have using my images. So I end up with an Apache
mod_rewrite script that's 40 lines long and only has about 20 blocked refererrers. The easy way if your host uses Apache is just a .htaccess file with
RewriteEngine on
RewriteCond %{REQUEST_URI} !/luvmoz.jpg$
RewriteCond %{HTTP_REFERER} !^http://(www\.)?moz.net.nz/.*$
RewriteRule \.(gif|jpg)$ /luvmoz.jpg [R,L]
Almost any host will have rewrite available, and it costs nothing to try

The above means that anyone hotlinking gets the luvmoz.jpg instead of the picture they want.
Since I have friends on just about all the common free hosts, I've had to do a deny list one item at a time, with myspace in particular being an "all myspace except these three" type entry. It's all a bit painful really. But it means that my useful stuff can be used, and I'm not helping gun nuts and neo-nazi's (unless you count a big blank gif as "helpful").