Solution #1 – Make sure you have the GD image library
Go to Quform → Settings on the WordPress menu and scroll down to the Server compatibility section, make sure the “GD Image Library” is Available. If it’s not, please ask your host to enable this library.
Solution #2 – CAPTCHA PHP script permissions
Some hosts will prevent access to the CAPTCHA PHP file which generates the image if the file permissions are not strict enough. Connect to your server via FTP and browse to wp-content/iphorm-form-builder/includes/captcha.php and change the file permissions to 644 (see this page for help on changing file permissions). Then set the permissions of ALL parent folders of this file to 755, so that would be these folders:
wp-content/iphorm-form-builder/includes/ wp-content/iphorm-form-builder/ wp-content/