One of our customer reported, that he see message "Please add support of gd2 extension in your php, otherwise e.g. captcha images will not work!" even if in his php is installed gd2.
He had installation of PHP5 on Windows Server.
Problem was fixed by installing latest version of php_gd2.dll
If you have same problem, please install php_gd2.dll delivered with your current version of PHP5.
Don't use older versions of this library with newer PHP release.