Include custom text in captcha code generated by ImageString - php

Question

I would like to have the ImageString in this script (that generates a captcha code) return the 5 digit numeric captcha code plus the text "is the code" (to help confuse spambots). Where would I modify this code to include my custom text in the image that is generated?
Thanks for any help on this.
<?php
session_start();
$md5_hash = md5(rand(0,99999));
$security_code = substr($md5_hash, 25, 5);
$enc = md5($security_code);
$_SESSION['captcha'] = $enc;
$width = 165;
$height = 30;
$image = ImageCreate($width, $height);
$white = ImageColorAllocate($image, 255, 255, 255);
$black = ImageColorAllocate($image, 0, 0, 0);
$grey = ImageColorAllocate($image, 200, 200, 200);
ImageFill($image, 0, 0, $white);
ImageString($image, 10, 7, 7, $security_code, $black);
header("Content-Type: image/png");
ImagePng($image);
ImageDestroy($image);
?>

Answer 1

Perhaps change
$security_code = substr($md5_hash, 25, 5);
to
$security_code = substr($md5_hash, 25, 5);
$security_code .= " is the code";
That will append your text onto the string, being passed into ImageString(). Try that & see how you go. You might want to increase the image width, as well.
One alternative: if your custom CAPTCHA's weak, you could go with a library -- which might be more secure, and provide you with updates & increased security as new versions are released.
I used SecurImage -- http://www.phpcaptcha.org/