<?php
   session_start();
   $width = 75; //Ukuran lebar
   $height = 25; //Tinggi
   $im = imagecreate($width, $height);
   $bg = imagecolorallocate($im, 0, 0, 0);
   $len = 5; //Panjang karakter 
   $chars = '0123456789abcdefghijklmnopqrstuvwxyz'; //Kombinasi huruf dan angka yang diacak
   $string = '';
   for ($i = 0; $i < $len; $i++) {
   $pos = rand(0, strlen($chars)-1);
   $string .= $chars{$pos};
   }
   $_SESSION['kodecap'] = $string; //hasil acak disimpan dalam session
//menambahkan titik2 gambar / noise
   $bgR = mt_rand(100, 200); $bgG = mt_rand(100, 200); $bgB = mt_rand(100, 200);
   $noise_color = imagecolorallocate($im, abs(255 - $bgR), abs(255 - $bgG), abs(255 - $bgB));
   for($i = 0; $i < ($width*$height) / 3; $i++) {
   imagefilledellipse($im, mt_rand(0,$width), mt_rand(0,$height), 3, rand(2,5), $noise_color);
   }
// proses membuat tulisan
   $text_color = imagecolorallocate($im, 240, 240, 240);
   $rand_x = rand(0, $width - 50);
   $rand_y = rand(0, $height - 15);
   imagestring($im, 12, $rand_x, $rand_y, $string, $text_color);
   header ("Content-type: image/png"); //Output format gambar
   imagepng($im);
?>