mod_rewrite help

[Cloak]

Hey folks, wondering if I can get some help with this problem.

I want to have certain pics show their thumbnailed equivalent when called from a website other than my own, how would I go about doing this? I don't want to blanked redirect to just one pic, I'd like it to go to the same pic but one level down in the thumbs dir.

I was thinking something like this would work, but doesn't:

RewriteEngine on
RewriteCond %{HTTP_REFERER} ^http://sitetoshowthumbs.com/$ [NC]
RewriteCond %{REQUEST_URI} ^/([0-9]+)/
RewriteRule ^/(.*)$ http://mysite.com/files/%1/thumbs/$1 [L]

The pictures would be in:

http://mysite.com/files/1/pic.jpg
http://mysite.com/files/1/thumbs/pic.jpg

I'd like to only do this for jpg, jpeg, png, and gif files.

Any pointers would be great, I just can't seem to get my head around how to do it. Thanks in advance.

[Cloak]

Got my answer, I figure I might as well share:

RewriteEngine on
RewriteCond %{HTTP_REFERER} ^[url]http://othersite.com/[/url] [NC]
RewriteCond %{REQUEST_URI} !^/files/([^/]+)/thumbs
RewriteCond %{REQUEST_URI} ^/files/([0-9]+)/([^.]+\.(jpg|gif|png))$ [NC]
RewriteRule ^.*$ /files/%1/thumbs/%2 [R]