htaccess hotlinking problem

Question

Hi! Iam fighting following problem with little success. I want to block hotlinking to images in static folder from other domains than my_domain.com

htaccess looks like this:

RewriteEngine on
RewriteCond %{HTTP_REFERER} !^$
RewriteCond %{HTTP_REFERER} !^http://(www\.)?my_domain\.com [NC]
RewriteRule \.(gif|jpe?g|js|css)$ - [F,NC,L]
RewriteRule ^(favicon\.ico)$ static/$1 [L]
RewriteCond $1 !^(index\.php|static|robots\.txt|7e3b7a5bafcb0fa8e8dfe3ea6aca9186\.txt)
RewriteRule ^(.*)$ /index.php/$1 [L]

Page is on CodeIgniter and it have static folder so images can be loaded for ex:

http://www.mydomain.com/static/somepic.jpg

but users are linking from other sites and eat my bandwidth fast.

Presented above htaccess doesnt work and I have NO idea why :(

Please help!