图像复制重新采样后显示的特殊字符

我制作了一个在我的网站上上传头像的脚本，它按预期工作（图像被调整大小并上传），但我不明白为什么页面重新加载后会显示这些特殊字符。

脚本：

//Session for test purpose
session_start();
$_SESSION['user']['id'] = 1337;
/*************************
    AVATAR UPLOAD
**************************/
$msg='';
if(isset($_POST['upload'])){

    $avatar = $_FILES['avatar']['name'];
    $avatar_tmp = $_FILES['avatar']['tmp_name'];
    if(!empty($avatar_tmp)){
        //Extension test
        $image = explode('.', $avatar);
        $image_ext = end($image);

        if(!in_array(strtolower($image_ext), array('png', 'gif', 'jpeg','jpg'))){
            $msg .= '<div class="error">Choosen file is not an image</div>';
        }
        //Mime test and image create
        else{
            $image_size = getimagesize($avatar_tmp);
            if($image_size['mime'] == 'image/jpeg'){
                $image_src = imagecreatefromjpeg($avatar_tmp);
            }
            elseif($image_size['mime'] == 'image/png'){
                $image_src = imagecreatefrompng($avatar_tmp);
            }
            elseif($image_size['mime'] == 'image/gif'){
                $image_src = imagecreatefromgif($avatar_tmp);
            }
            else{
                $msg .= '<div class="error">Choosen file is not an image</div>';
            }
        }
        //No error -> resize and upload
        if(empty($msg)){
            $image_width = 150;
            if($image_size[0] <= $image_width){
                $image_finale = $image_src;
            }
            else{
                $new_width[0] = $image_width;
                $new_height[1] = ($image_size[1] / $image_size[0]) * $image_width;
                $image_finale = imagecreatetruecolor($new_width[0], $new_height[1]);
                imagecopyresampled($image_finale, $image_src, 0, 0, 0, 0, $new_width[0], $new_height[1], $image_size[0], $image_size[1]);
            }
            imagejpeg($image_finale, 'img/' . $_SESSION['user']['id'] . '.jpg');
            imagejpeg($image_finale);
            $msg .= '<div class="success">Avatar uploaded</div>';
        }
    }
}

显示字符：

ÿØÿàJFIFÿþ>CREATOR: gd-jpeg v1.0 (using IJG JPEG v90), default quality ÿÛC     $.' ",#(7),01444'9=82<.342ÿÛC ...    

提前感谢您的帮助。