Captcha generator with session!

<?php
session_start(); //Set Sessions Available To Set & Get
$width = 100; // Width of the Image
$height = 60; //Height of the Image
$textCNG = substr(str_shuffle(str_repeat('ABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789',11)),0,rand(4,7)); //Created random Text
$text = $textCNG; //Set Final Text to Randomized Text
$_SESSION['captcha'] = $text; //Set Session Text
header ("Content-type: image/png"); //Set HTML Header

$img = ImageCreate ($width, $height) or die ("Cannot Initialize new GD image stream"); //Create New Image
$background_color = ImageColorAllocate ($img, 255, 255, 255); //Set Background Color
$style_color = ImageColorAllocate ($img, 59, 59, 59); //Set Style Color
$text_color = ImageColorAllocate ($img, 120, 95, 95); //Set Text Color

for($i >= 0; $i <= rand(2,5); $i++){
    imageline($img,0,rand()%$height,$width,rand()%$height,$style_color);//Set Random Lines Into The Image
}
for($i >= 0; $i <= rand(220,440); $i++){
    imagesetpixel($img,rand()%$width,rand()%$height,$style_color); //Set Dots Into The Image
}

imagestring($img, 5, 22, 22, $text, $text_color); //Write Image Text


ImagePng ($img); //Show the image

imagedestroy($img); //Destroy the image
?>