session_start();

$image = imagecreatetruecolor(100, 30); //創建一個100×30的畫布
$white = imagecolorallocate($image,255,255,255);//白色
imagefill($image,0,0,$white);//覆蓋黑色畫布

$session = ""; //空變量 ，存放驗證碼
for($i=0;$i4;$i++){
 $size = 6;
 $x = $i*25+mt_rand(5,10);
 $y = mt_rand(5,10);
 $sizi_color = imagecolorallocate($image,mt_rand(80,220),mt_rand(80,220),mt_rand(80,220));
 $char = join("",array_merge(range('a','z'),range('A','Z'),range(0,9)));
 $char = str_shuffle($char);
 $char = substr($char,0,1);
 imagestring($image,$size,$x,$y,$char,$sizi_color);
 $session .= $char ; //把驗證碼的每一個值賦值給變量
}
 $_SESSION['session'] = $session; //這個變量的值與用戶輸入的值相等

for($k=0;$k200;$k++){
 $rand_color = imagecolorallocate($image,mt_rand(50,200),mt_rand(50,200),mt_rand(50,200));
 imagesetpixel($image,mt_rand(1,99),mt_rand(1,29),$rand_color);
}
for($n=0;$n5;$n++){
 $line_color = imagecolorallocate($image,mt_rand(80,220),mt_rand(80,220),mt_rand(80,220));
 imageline($image,mt_rand(1,99),mt_rand(1,29),mt_rand(1,99),mt_rand(1,29),$line_color);
}
header('content-type:image/png');//設置文件輸出格式
imagepng( $image ); //以png格式輸出$image圖像
imagedestroy( $image ); //銷毀圖像

if(isset($_POST['session'])){
 session_start();
 if(strtolower($_POST['session'])==strtolower($_SESSION['session'])){
  echo'font color="#0000CC">輸入正確/form>';
 }else{
  echo 'font color="#CC0000">b>輸入錯誤/b>/font>';
 }
 exit();
}

!DOCTYPE html>
html>
head>
 meta charset="utf-8"/>
 title>確認驗證碼/title>
/head>
body>
 form method="post" action="./tushu.php">
 p>驗證碼圖片:img id="img" border="1" src="http://localhost//xxx.php" width="100" height="30">/p>
 a href="javascript:void(0)" rel="external nofollow"  onclick="document.getElementById('img').src='http://localhost//xxx.php'">看不清？換一個/a>
 p>請輸入圖片中的驗證碼：input type="text" name="session" value=""/>/p>
 p>input type="submit" value="提交" style="padding:6px 10px;">/p>
 /form>
/body>
/html>