php 验证码实现

$width=80;
$height=28;
$image=imagecreatetruecolor($width,$height);
$white=imagecolorallocate($image,255,255,255);//白色

$black=imagecolorallocate($image,0,0,0);//黑色
//用填充矩形填充画布

imagefilledrectangle($image,1,1,$width-2,$height-2,$white);
$type=1;
$length=4;
$chars=buildRandomString($type,$length);
$sess_name="verify";
$_SESSION['sess_name']=$chars;
$fontfiles=array("MSYH.TTF","MSYHBD.TTC","SIMLI.TTF","SIMSUN.TTC","SIMYOU.TTF","STZHONGS.TTF");
//这是字体，cmd 输入fonts可以查看到自己电脑里面的字体 然后拷贝到自己项目的文件夹下
$fontfile="../fonts/".$fontfiles[mt_rand(0,count($fontfiles)-1)];
//随机取出一个字体格式 0-数组长度减一
for($i=0;$i<$length;$i++)
{
$size=mt_rand(14,18);//产生一个随机的数字大小
$angle=mt_rand(-15,15);//产生一个随机的角度
$x=5+$i*$size;//一个横坐标
$y=mt_rand(20,26);
$color=imagecolorallocate($image,mt_rand(50,90),mt_rand(80,200),mt_rand(90,180));//产生的随机颜色
$text=substr($chars,$i,1);
imagettftext($image,$size,$angle,$x,$y,$color,$fontfile,$text);
}
$pixel=50;
if($pixel)
{
for($i=0;$i<50;$i++)
{
imagesetpixel($image,mt_rand(0,$width-1),mt_rand(0,$height-1),$black) ;
}
//这个for循环的目的是画出小黑点
}
$line=10;
if($line)
{
for($i=1;$i<10;$i++)
{
imageline($image,mt_rand(0,$width-1),mt_rand(0,$height-1),mt_rand(0,$width-1),mt_rand(0,$height-1),$color);
//画的横线也为随机颜色
}
}

header("content-type:image/gif");
imagegif($image);
imagedestory($image);

function buildRandomString($type=1,$length=4)
{

//产生随机字符串
//$type = 1;
//$length = 4;//产生4位验证码
if ($type == 1) {
$chars = join("", range(0, 9));
} elseif ($type == 2) {
$chars = join("", array_merge(range("a", "z"), range("A", "Z")));
} elseif ($type == 3) {
$chars = join("", array_merge(range("a", "z"), range("A", "Z"), range("0", "9")));
}

if ($length > strlen($chars))  //产生的长度不够
{
exit("字符串长度不够");
}
$chars = str_shuffle($chars);//随意打乱
return substr($chars, 0, $length);

}//函数在此结束