Session Captcha Error

Kenapa ya session captchanya ada dua (berbeda). Cek gambar:

Kode script sbb.

<?php
session_start();
header("Content-type: image/jpg");

//generate Code
function RandomCode($max){
//Huruf dan angka yang akan di acak
$char = array("0","1","2","3","4","5","6","7","8","9","0","1","2","3","4","5","6","7","8","9","0","1","2","3","4","5","6","7","8","9");
$keys = array();
while(count($keys) < $max) {
$x = mt_rand(0, count($char)-1);
if(!in_array($x, $keys)) {
$keys[] = $x;
}
}
$random='';
foreach($keys as $key => $val){
$random .= $char[$val];
}
return $random;
}

$font='Neon80s.ttf'; //setting font yang akan digunakan
//$images='cap.jpg'; gambar yang akan digunakan sebagai background
$im = imagecreatefromjpeg("cap.jpg")or die("Cannot Initialize new GD image stream"); //gambar yg akan jadi bahan dasar
$fontcolor = imagecolorallocate($im, 255, 250, 255); //menentukan warna text rgb
//Generate kode yang akan dituliskan pada gambar sebanyak 5
$text=RandomCode(5);
//Buat sessi untuk pengecekan pada halaman lain
$_SESSION['captcha']=$text;
//Tuliskan text pada gambar
imagettftext($im, 72, 0, 20,110, $fontcolor, $font, $text); //(gambar, ukuran, kemiringan, margin-kiri, margin-atas, warna text, jenis font, teks)
imagejpeg($im);
imagedestroy($im);
?>

Apakah ada yg salah??