php生成圖片驗證碼

<?php
/**
 * vCode(m,n,x,y) m個數字  顯示大小爲n   邊寬x   邊高y
 * http://blog.qita.in
 * 自己改寫記錄session $code
 */
session_start(); 
vCode(4, 15); //4個數字，顯示大小爲15

function vCode($num = 4, $size = 20, $width = 0, $height = 0) {
	!$width && $width = $num * $size * 4 / 5 + 5;
	!$height && $height = $size + 10; 
	// 去掉了 0 1 O l 等
	$str = "23456789abcdefghijkmnpqrstuvwxyzABCDEFGHIJKLMNPQRSTUVW";
	$code = '';
	for ($i = 0; $i < $num; $i++) {
		$code .= $str[mt_rand(0, strlen($str)-1)];
	} 
	// 畫圖像
	$im = imagecreatetruecolor($width, $height); 
	// 定義要用到的顏色
	$back_color = imagecolorallocate($im, 235, 236, 237);
	$boer_color = imagecolorallocate($im, 118, 151, 199);
	$text_color = imagecolorallocate($im, mt_rand(0, 200), mt_rand(0, 120), mt_rand(0, 120)); 
	// 畫背景
	imagefilledrectangle($im, 0, 0, $width, $height, $back_color); 
	// 畫邊框
	imagerectangle($im, 0, 0, $width-1, $height-1, $boer_color); 
	// 畫干擾線
	for($i = 0;$i < 5;$i++) {
		$font_color = imagecolorallocate($im, mt_rand(0, 255), mt_rand(0, 255), mt_rand(0, 255));
		imagearc($im, mt_rand(- $width, $width), mt_rand(- $height, $height), mt_rand(30, $width * 2), mt_rand(20, $height * 2), mt_rand(0, 360), mt_rand(0, 360), $font_color);
	} 
	// 畫干擾點
	for($i = 0;$i < 50;$i++) {
		$font_color = imagecolorallocate($im, mt_rand(0, 255), mt_rand(0, 255), mt_rand(0, 255));
		imagesetpixel($im, mt_rand(0, $width), mt_rand(0, $height), $font_color);
	} 
	// 畫驗證碼
	@imagefttext($im, $size , 0, 5, $size + 3, $text_color, 'c:\\WINDOWS\\Fonts\\simsun.ttc', $code);
	$_SESSION["VerifyCode"]=$code; 
	header("Cache-Control: max-age=1, s-maxage=1, no-cache, must-revalidate");
	header("Content-type: image/png;charset=gb2312");
	imagepng($im);
	imagedestroy($im);
} 

?>