I'm getting a 500 error on the page that displays the captcha image which makes it hard to debug. It could be a permission issue that is preventing the image to display.
For now, please try adding these lines of code to the
$font = realpath($font);
under this line of code:
$font = isset($_GET['font']) && $_GET['font'] != "" ? $_GET['font'] : 'Fonts/MOM_T___.TTF';
if you still having an issue, please contact your hosting provider to see if they could provide more information about the error on your page.