网站为了防止用户利用机器人自动注册、登录、灌水，采用了验证码技术。所谓验证码，就是将一串随机产生的数字或符号，生成一幅图片， 图片里加上一些干扰象素（防止OCR），由用户肉眼识别其中的验证码信息，输入表单提交网站验证，验证成功后才能使用某项功能。这里展示了PHP实现漂亮的验证码功能，具体代码如下：

<?php

class Imagecode{

private $width ;

private $height;

private $counts;

private $distrubcode;

private $fonturl;

private $session;

function __construct($width = 120,$height = 30,$counts = 5,$distrubcode="1235467890qwertyuipkjhgfdaszxcvbnm",$fonturl="C:\Windows\Fonts\TektonPro-BoldCond.otf"){

$this->width=$width;

$this->height=$height;

$this->counts=$counts;

$this->distrubcode=$distrubcode;

$this->fonturl=$fonturl;

$this->session=$this->sessioncode();

session_start();

$_SESSION['code']=$this->session;

}

function imageout(){

$im=$this->createimagesource();

$this->setbackgroundcolor($im);

$this->set_code($im);

$this->setdistrubecode($im);

ImageGIF($im);

ImageDestroy($im);

}

private function createimagesource(){

return imagecreate($this->width,$this->height);

}

private function setbackgroundcolor($im){

$bgcolor = ImageColorAllocate($im, rand(200,255),rand(200,255),rand(200,255));//±³¾°ÑÕÉ«

imagefill($im,0,0,$bgcolor);

}

private function setdistrubecode($im){

$count_h=$this->height;

$cou=floor($count_h*2);

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

$x=rand(0,$this->width);

$y=rand(0,$this->height);

$jiaodu=rand(0,360);

$fontsize=rand(8,15);

$fonturl=$this->fonturl;

$originalcode = $this->distrubcode;

$countdistrub = strlen($originalcode);

$dscode = $originalcode[rand(0,$countdistrub-1)];

$color = ImageColorAllocate($im, rand(40,140),rand(40,140),rand(40,140));

imagettftext($im,$fontsize,$jiaodu,$x,$y,$color,$fonturl,$dscode);

}

}

private function set_code($im){

$width=$this->width;

$counts=$this->counts;

$height=$this->height;

$scode=$this->session;

$y=floor($height/2)+floor($height/4);

$fontsize=rand(30,35);

$fonturl="C:\Windows\Fonts\AdobeGothicStd-Bold.otf";//$this->fonturl;

$counts=$this->counts;

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

$char=$scode[$i];

$x=floor($width/$counts)*$i+8;

$jiaodu=rand(-20,30);

$color = ImageColorAllocate($im,rand(0,50),rand(50,100),rand(100,140));

imagettftext($im,$fontsize,$jiaodu,$x,$y,$color,$fonturl,$char);

}

}

private function sessioncode(){

$originalcode = $this->distrubcode;

$countdistrub = strlen($originalcode);

$_dscode = "";

$counts=$this->counts;

for($j=0;$j<$counts;$j++){

$dscode = $originalcode[rand(0,$countdistrub-1)];

$_dscode.=$dscode;

}

return $_dscode;

}

}

Header("Content-type: image/GIF");

$imagecode=new Imagecode(160,50);

$imagecode->imageout();

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