Apache Rewrite - hosted images exception

Apache Rewrite - hosted images exception

I use...
RewriteCond %{HTTP_REFERER} .
RewriteCond %{HTTP_REFERER} !^http://([^.]+\.)?graphium\.com/ [NC]
RewriteCond %{HTTP_USER_AGENT}
!(googlebot–image|msnbot|psbot|yahoo–mmcrawler) [NC]
RewriteRule \.(bmp|gif|jpe?g|png)$ /images/hotlink.$1 [L]
...in my httpd.conf to stop people linking directly to any images on my
site. Mostly, it has always, does and, I trust, always will, Just Work.
But I want to amend the rules to allow for a named directory to contain
linkable images. Just the one directory (lets call it
/public_html/pictures) - but I can't see how to amend my ruleset to allow
this.
Any suggestions, anyone?