Q:

Failed to generate captcha image, content has already been output

i m using secureimage solution to generate captcha code
i have this error on chrom console 

Resource interpreted as Image but transferred with MIME type text/html

and when entring on this url directly used as image src

securimage_show.php?sid=fa5e1eb19c3a534885632e

i have this error

Failed to generate captcha image, content has already been output. 
  This is most likely due to misconfiguration or a PHP error was sent to
  the browse

someone have idea ? 
Note: it works for me in localhost wampserver but not on remote server
Edit:
the code from the captcha opensource code generating php errors :
 protected function output()
{
    if ($this->canSendHeaders() || $this->send_headers == false) {
        if ($this->send_headers) {
            // only send the content-type headers if no headers have been output
            // this will ease debugging on misconfigured servers where warnings
            // may have been output which break the image and prevent easily viewing
            // source to see the error. 
            header("Expires: Mon, 26 Jul 1997 05:00:00 GMT");
            header("Last-Modified: " .  gmdate("D, d M Y H:i:s") . " GMT");
            header("Cache-Control: no-store, no-cache, must-revalidate");
            header("Cache-Control: post-check=0, pre-check=0", false);
            header("Pragma: no-cache");
        }

        switch ($this->image_type) {
            case self::SI_IMAGE_JPEG:
                if ($this->send_headers) header("Content-Type: image/jpeg");
                imagejpeg($this->im, null, 90);
                break;
            case self::SI_IMAGE_GIF:
                if ($this->send_headers) header("Content-Type: image/gif");
                imagegif($this->im);
                break;
            default:
                if ($this->send_headers) header("Content-Type: image/png");
                imagepng($this->im);
                break;
        }
    } else {
        echo '<hr /><strong>'
            .'Failed to generate captcha image, content has already been '
            .'output.<br />This is most likely due to misconfiguration or '
            .'a PHP error was sent to the browser.</strong>';
    }

    imagedestroy($this->im);
    restore_error_handler();

    if (! $this->no_exit) exit;
}

A:

Quick Fix:
Just replace canSendHeaders function in securimage.php file
From
protected function canSendHeaders() {

    if (headers_sent()) {

        // output has been flushed and headers have already been sent
        return false;
    } else if (strlen((string) ob_get_contents()) > 0) {
        // headers haven't been sent, but there is data in the buffer that will break image and audio data
        return false;
    }

    return true;
}

To 
protected function canSendHeaders() {

    ob_get_clean();

    if (headers_sent()) {

        // output has been flushed and headers have already been sent
        return false;
    } else if (strlen((string) ob_get_contents()) > 0) {
        // headers haven't been sent, but there is data in the buffer that will break image and audio data
        return false;
    }

    return true;
}

