<?php

header("Content-type: image/png");

session_start();

$authnum = ‘‘;

$str = ‘abcdefghigklmnopqrstuvwxyz1234567890‘;

$strLength = strlen($str);

for($i=0;$i<=4;$i++)

{

    $num = rand(0, $strLength -1);

    $authnum .= $str[$num];

}

    $_SESSION[‘authnum‘] = $authnum;

    srand((double)microtime()*1000000);

    $im = imagecreate(200, 100);

    $gary = imagecolorallocate($im, 200, 200, 100);

    $white = imagecolorallocate($im, 255, 255, 255);

    imagefill($im, 10, 5, $gary);

    $li = imagecolorallocate($im, 150, 150, 150);

    for($i =0;$i<3;$i++)//绘制三条干扰线

    {

       imageline($im, rand(0, 20), rand(0, 100), rand(180, 200), rand(0, 100), $li);

       //起点的x尽量靠左边，y任意，终点尽量靠右边，y任意

    }

    for($i=0;$i<strlen($_SESSION[‘authnum‘]);$i++)//绘制四个字符

    {

       $strcolor= imagecolorallocate($im, mt_rand(0, 100), mt_rand(50, 150), mt_rand(100, 200));

       $fontsize = mt_rand(10, 20);

       $x = mt_rand(1,20)+200*$i/4;

       $y = mt_rand(1, 50);

       imagestring($im, $fontsize, $x, $y, $_SESSION[‘authnum‘][$i], $strcolor);

    }

imagepng($im);

imagedestroy($im);

?>

运行效果如图所示：