简单的php图片验证码_PHP

一个简单的php生成的图片验证码，带表单，验证码生成代码，以及验证程序

image.php
<?php 
header("Content-type: image/png"); 
$string = "abcdefghijklmnopqrstuvwxyz0123456789"; 
for($i=0;$i<6;$i++){ 
    $pos = rand(0,36); 
    $str .= $string{$pos}; 
} 
$img_handle = ImageCreate (60, 20) or die ("Cannot Create image"); 
//Image size (x,y) 
$back_color = ImageColorAllocate($img_handle, 255, 255, 255); 
//Background color RBG 
$txt_color = ImageColorAllocate($img_handle, 0, 0, 0); 
//Text Color RBG 
ImageString($img_handle, 31, 5, 0, $str, $txt_color); 
Imagepng($img_handle); 
session_start(); 
$_SESSION['img_number'] = $str; 
?>
form.php
<form action="result.php" method="post">
    <img alt="Random Number" src="image.php"> 
    <input type="text" name="num"><br>
    <input type="submit" name="submit" value="Check">
</form>
result.php
<?php 
session_start(); 
if($_SESSION['img_number'] != $_POST['num']){ 
    echo'The number you entered doesn't match the image.<br> 
    <a href="form.php">Try Again</a><br>'; 
}else{ 
    echo'The numbers Match!<br> 
    <a href="form.php">Try Again</a><br>'; 
} 
?> 
[url=http://phpsnips.com/examples/CAPTCHA/form.php]Example[/url]