I created a captcha just now, and it works PERFECTLY on my own server. On the school's server, it doesn't generate an image. Why might this be? The difference in code is one line.

*Edit:*Originally, it was working, but I deleted the directory by mistake and I do not know why did it suddenly work in the first place.

Source code on school server:

  <?php
            session_save_path("/ichanged/this/path/for/this/post/");
        session_start();

     $img=imagecreatefromjpeg("bg.jpg"); 

     if( empty($_SESSION['captcha_numbers']) ) {
      $captcha_numbers = 'error'; 
     } else {
      $captcha_numbers = $_SESSION['captcha_numbers'];   
     }
     $image_numbers=$captcha_numbers; 

     $red=rand(100,150); 
     $green=rand(100,255);
     $blue=rand(100,255);

     $color=imagecolorallocate($img,255-$red,255-$green,255-$blue);

     $text=imagettftext($img,12,rand(-7,7),rand(10,20),rand(20,30),$color,"fonts/M04.TTF",$image_numbers);

     header("Content-type:image/jpeg");
     header("Content-Disposition:inline ; filename=secure.jpg"); 
     imagejpeg($img);

    ?>

Source code on my server:

<?php


 session_start();

     $img=imagecreatefromjpeg("bg.jpg"); 

     if( empty($_SESSION['captcha_numbers']) ) {
      $captcha_numbers = 'error'; 
     } else {
      $captcha_numbers = $_SESSION['captcha_numbers'];   
     }
     $image_numbers=$captcha_numbers; 

     $red=rand(100,150); 
     $green=rand(100,255);
     $blue=rand(100,255);

     $color=imagecolorallocate($img,255-$red,255-$green,255-$blue);

     $text=imagettftext($img,12,rand(-7,7),rand(10,20),rand(20,30),$color,"fonts/M04.TTF",$image_numbers);

     header("Content-type:image/jpeg");
     header("Content-Disposition:inline ; filename=secure.jpg"); 
     imagejpeg($img);

    ?>