how to forbidden other site stealing my forum attachment ?

[二戒]

Hello everyone,

My forum posts and attachments have been stolen much more by other site.
and I write a nginx rule to prevent, without success, please guide.

example this forum:
http://dysmyh.com/thread-41217-1-1.html

and my attachments url as
http://www.cnprint.org/bbs/attachment.php?attachmentid=205810&d=1359965752

and my forum domain is www.cnprint.org, and forum script put into /bbs/
directory.

now I forbidden others site show my attachment, this rule don't work,
please help me.

I think should this line "location ~* ^/bbs/attachment+\.php?$" has
mistake, but I can't resolve it.

location ~* ^/bbs/attachment+\.php?$
{
valid_referers none blocked *.cnprint.org server_names ~\.google\.
~\.baidu\. ~\.360\. ~\.bing\.;
if ($invalid_referer) {
# return 403;
rewrite ^.*$ http://www.cnprint.org;
}
}
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