php 生成图形验证码（大小写字母与数字混合）

[php]代码库

<?php
	header("content-type:image/png");
	$num = $_GET['num'];
	$imagewidth=60;
	$imageheight=18;
	srand(microtime() * 100000);

	$numimage = imagecreate($imagewidth,$imageheight);
	imagecolorallocate($numimage,183,180,83);
	for($i=0;$i<strlen($num);$i++){
		$font = mt_rand(3,5);
		$x = mt_rand(1,8)+$imagewidth*$i/4;
		$y = mt_rand(1,$imageheight/3);
		$color=imagecolorallocate($numimage,mt_rand(0,50),mt_rand(0,150),mt_rand(0,255));
		imagestring($numimage,$font,$x,$y,$num[$i],$color);
	}
	imagepng($numimage);
	imagedestroy($numimage);
?>



调用方法：
<?php
	session_start();
	include_once 'conn/conn.php';
	$pattern = '1234567890abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLOMNOPQRSTUVWXYZ';
	$num = null;
	for($i = 0; $i < 4; $i++) {
        $num .= $pattern{mt_rand(0, 61)};
	}	
?>

<div> 验证码：
  <input id="lgchk" type="text" />
  <img src="valcode.php?num=<?php echo $num; ?>" width="55" height="18" /> </div>

[代码运行效果截图]