how do I override htaccess rule for a specific directory

I have created following rule in the .htaccess file located at t开发者_运维技巧he root of my application as (like this, app_name/.htaccess )

Options +FollowSymLinks
RewriteEngine on
RewriteRule ^([^/]*)/([^/]*)$ /index.php?client=$1&page=$2 [L]

The problem now is that I am not able to access the "captcha class" located in the classes folder (http://app_name/classes/captcha.php?args=xyz&arg1=abc) of the web application directory. What is the best solution to this problem. Please throw some light.

Thanks

RewriteEngine on
RewriteCond %{REQUEST_URI} !^/classes/captcha.php
RewriteRule ^([^/]*)/([^/]*)$ /index.php?client=$1&page=$2 [L]