TOPIC: Captcha NOT Visible

I've security image component 5.1.2 for joomla 1.5.17. When i install !jcomment , the security image in antispam field isn't visible.

I've set chmod for com_comment folder to 755 (and not work) and 777 (default, and nont work).

This is my php info :
System Info

What can i do?

Thanks

May we get to see your website? Perhaps there is fatal error recorded in the error log.