php写简单的随机验证码

 跟着教程写随机的数字验证码？

<?php

session_start();

//创建随机码

$_nmsg = '';

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

    $_nmsg .= dechex(mt_rand(0,15)); 

}

//保存在session

$_SESSION['code'] = $_nmsg;



//创建一个真彩色图像

$_width =75;

$_height = 25;

$_img = imagecreatetruecolor($_width, $_height);

//白色

$_white = imagecolorallocate($_img, 255, 255, 255);

//填充

imagefill($_img, 0, 0, $_white);

//随机画出6个线条

for($i = 0; $i<6; $i++){

    $_md_color  = imagecolorallocate($_img,mt_rand(0, 255),mt_rand(0, 255), mt_rand(0, 255));

    imageline($_img, mt_rand(0, 75),  mt_rand(0, 75),  mt_rand(0, 75),  mt_rand(0, 75),$_md_color); 

}

//随机雪花

for($i = 0; $i<100;$i++){

    $_md_color = imagecolorallocate($_img, mt_rand(200, 255), mt_rand(200, 255), mt_rand(200, 255));

    imagestring($_img, 1, mt_rand(1, $_width), mt_rand(1, $_height), '*', $_md_color);

}

//黑色边框

$_black = imagecolorallocate($_img, 0, 0, 0);

imagerectangle($_img, 0, 0, $_width-1, $_height-1, $_black);

//输出验证码

for($i = 0;$i<strlen($_SESSION['code']);$i++){

    $_mt_color = imagecolorallocate($_img, mt_rand(0, 100), mt_rand(0, 150), mt_rand(0, 200));

    imagestring($_img, mt_rand(3, 5), $i*$_width/4+mt_rand(1, 10), mt_rand(1, $_height/2), $_SESSION['code'][$i],$_mt_color);  

}

header('Content-Type:image/png');

imagepng($_img);

//销毁

imagedestroy($_img);



?>