My Captcha image is not loading

[#1]

I need some help, my website feedback form has a captcha image to stop spam.. the form works but but the captcha image is not loading thereby preventing anyone from entering a valid code to submit.. see here - http://ccgi.cookuk.plus.com/astro/add_feedback.php
Im using the php_self function in my form using the POST method.
Here is the line of code for the captcha part of the form...
print "<td width=80>Security Code:</td>";
print "<td width=470><img src=CaptchaSecurityImages.php>&nbsp;<input id=security_code name=security_code type=text /></td>";
CaptchaSecurityImages.php is in the same directory as this form page. As well as the monofont.ttf file.
I've even tried changing the permissions of these files to 777 (read, write, execute on all levels). Still the image does not load.
Any advice or more info needed?
thanks
Matt

[#2]

Looks like a 500 error. Check out the faq, particularly sections 6 and 8. Perhaps check  the setup with a simple phpinfo() script, just to be sure.
Gabe