验证码图像没有生成

I had uploaded my web app on different domain. I am having problem with captcha. It's not loading, instead it is showing a broken image icon. It was not even showing any error so I add error_reporting and ini_set function.

public function captcha() {
        error_reporting(E_ALL);
        ini_set('display_errors', 1);
        $string = substr(number_format(time() * rand(), 0, '', ''), 0, 5);
        $_SESSION["captcha_val"] = $string;
        $captcha = imagecreatefrompng(base_url('resources/images/captcha.png'));
        $black = imagecolorallocate($captcha, 28, 28, 28);
        imagestring($captcha, 5, 20, 10, $string, $black);
        $_SESSION['captcha_key'] = $string;
        //header("Content-type: image/png");
        //imagepng($captcha);

    }

now its showing following four errors:

Message: imagecreatefrompng(): https:// wrapper is disabled in the server configuration by allow_url_fopen=0

Filename: web/inquiry.php

Line Number: 21

Message: imagecreatefrompng(https://creativersity.in/eassist/resources/images/captcha.png): failed to open stream: no suitable wrapper could be found

Filename: web/inquiry.php

Line Number: 21

Message: imagecolorallocate() expects parameter 1 to be resource, boolean given

Filename: web/inquiry.php

Line Number: 22

Message: imagestring() expects parameter 1 to be resource, boolean given

Filename: web/inquiry.php

Line Number: 23

Please help me with this