php Captcha разрешение отклонено

<?php
session_start();
if(isset($_POST["captcha"])) {
if(($_SESSION['captcha_code'] == $_POST['captcha']) && (!empty($_SESSION['captcha_code'])) ) {
//Passed!
$captcha_msg="Thank you";
}else{
// Not passKed 8-(
$captcha_msg="invalid code";
if(isset($_POST["MM_insert"])){
unset($_POST["MM_insert"]);
}
if(isset($_POST["MM_update"])){
unset($_POST["MM_update"]);
}
}
}
class CaptchaImage {
var $font = "verdana.ttf";
function hex_to_dec($hexcolor){
//convert hex hex values to decimal ones
$dec_color=array('r'=>hexdec(substr($hexcolor,0,2)),'g'=>hexdec(substr($hexcolor,2,2)),'b'=>hexdec(substr($hexcolor,4,2)));
return $dec_color;
}
function generateCode($characters) {
/* list all possible characters, similar looking characters and vowels have been removed */
$possible = '23456789bcdfghjkmnpqrstvwxyz';
$code = '';
$i = 0;
while ($i < $characters) {
$code .= substr($possible, mt_rand(0, strlen($possible)-1), 1);
$i++;
}
return $code;
}
function CaptchaImage($width='120',$height='30',$characters='6',$hex_bg_color='FFFFFF',$hex_text_color="FF0000",$hex_noise_color="CC0000", $img_file='captcha.jpg') {
$rgb_bg_color=$this->hex_to_dec($hex_bg_color);
$rgb_text_color=$this->hex_to_dec($hex_text_color);
$rgb_noise_color=$this->hex_to_dec($hex_noise_color);
$code = $this->generateCode($characters);
/* font size will be 60% of the image height */
$font_size = $height * 0.60;
$image = @imagecreate($width, $height) or die('Cannot Initialize new GD image stream');
/* set the colours */
$background_color = imagecolorallocate($image, $rgb_bg_color['r'], $rgb_bg_color['g'],$rgb_bg_color['b']);
$text_color = imagecolorallocate($image, $rgb_text_color['r'], $rgb_text_color['g'],$rgb_text_color['b']);
$noise_color = imagecolorallocate($image, $rgb_noise_color['r'], $rgb_noise_color['g'],$rgb_noise_color['b']);
/* generate random dots in background */
for( $i=0; $i<($width*$height)/3; $i++ ) {
imagefilledellipse($image, mt_rand(0,$width), mt_rand(0,$height), 1, 1, $noise_color);
}
/* generate random lines in background */
for( $i=0; $i<($width*$height)/150; $i++ ) {
imageline($image, mt_rand(0,$width), mt_rand(0,$height), mt_rand(0,$width), mt_rand(0,$height), $noise_color);
}
/* create textbox and add text */
$textbox = imagettfbbox($font_size, 0, $this->font, $code);
$x = ($width - $textbox[4])/2;
$y = ($height - $textbox[5])/2;
imagettftext($image, $font_size, 0, $x, $y, $text_color, $this->font , $code);
/* save the image */
imagejpeg($image,$img_file);
imagedestroy($image);
echo "<img src=\"$img_file?".time()."\" width=\"$width\" height=\"$height\" alt=\"security code\" id=\"captchaImg\">";
$_SESSION['captcha_code'] = $code;
}

}

Предупреждение: imagejpeg (): недопустимый 2-й параметр, это должно быть имя файла или поток в /Applications/XAMPP/xamppfiles/htdocs/chunyiu/memberAdd.php в строке 63.

Почему сказано, что строка 63 imagejpeg ($ image, $ img_file); неверный 2-й параметр