CAPTCHA not work

[kolombaru]

This user has been denied support.

Mybb Captcha is not work, I've modificated newthread.php and newreply.php to show captcha code when user or guest creating a post. that modification like this:

newthread.php and newreply.php and find:

    // Show captcha image for guests if enabled
    if($mybb->settings['captchaimage'] == 1 && function_exists("imagepng") && !$mybb->user['uid']) 

change that code to;

    // Show captcha image for guests and users if enabled
    if($mybb->settings['captchaimage'] == 1 && function_exists("imagepng"))

I've tried it and work in localhost, but not working on my site other (captcha image done but no function if user <just user> create a new post ). So what is the problem?

Anyone help me, my site http://www.kolombaru.com and you can try that by register and create a post...
thanks before

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No one couldn't help?