php验证码

网上搜罗也可以搜罗一大堆，但是代码都不是很优美，我个人就这么认为，因为刚开始写php，经常要去官网看看文档，php的文档真是个宝库，只要你花点时间看下，你就会发现很多优美的程序方法。这个验证码是我组织的：

<?php
session_start();

// Generate a random character string
function rand_str($length = 32, $chars = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz1234567890')
{
    // Length of character list
    $chars_length = (strlen($chars) - 1);

    // Start our string
    $string = $chars{rand(0, $chars_length)};
   
    // Generate random string
    for ($i = 1; $i < $length; $i = strlen($string))
    {
        // Grab a random character from our list
        $r = $chars{rand(0, $chars_length)};
       
        // Make sure the same two characters don't appear next to each other
        if ($r != $string{$i - 1}) $string .=  $r;
    }
   
    // Return the string
    return $string;
}
$authnum_session=rand_str(4);

$_SESSION["authnum_session"]=$authnum_session;
//生成图片
$im=imagecreate(60,20);
$blank=imagecolorallocate($im,0,0,0);
$white=imagecolorallocate($im,255,255,255);
$gray=imagecolorallocate($im,200,200,200);
imagefill($im,68,30,$gray);
$li=imagecolorallocate($im,220,220,220);
for($j=0;$j<3;$j++){
 imageline($im,rand(0,30),rand(0,21),rand(20,40),rand(0,21),$li);
}
for($z=0;$z<90;$z++){
 imagesetpixel($im,rand()%70,rand()%30,$gray);
}
imagestring($im,5,12,5,$authnum_session,$white);
header("Content-Type:image/png");
imagepng($im);
?>