How to implement verification code generator in php

<?php
$iC = new idCode(5,60,30);
$iC->createPNG();

class idCode{
  private $words = array(&#39;a&#39;,&#39;b&#39;,
  &#39;c&#39;,&#39;d&#39;,&#39;e&#39;,&#39;f&#39;,&#39;g&#39;,&#39;h&#39;,&#39;i&#39;,&#39;j&#39;,&#39;k&#39;,&#39;l&#39;,
  &#39;m&#39;,&#39;n&#39;,&#39;o&#39;,&#39;p&#39;,&#39;q&#39;,&#39;r&#39;,&#39;s&#39;,&#39;t&#39;,&#39;u&#39;,&#39;v&#39;,
  &#39;w&#39;,&#39;x&#39;,&#39;y&#39;,&#39;z&#39;,&#39;A&#39;,&#39;B&#39;,&#39;C&#39;,&#39;D&#39;,&#39;E&#39;,&#39;F&#39;,
  &#39;G&#39;,&#39;H&#39;,&#39;I&#39;,&#39;J&#39;,&#39;K&#39;,&#39;L&#39;,&#39;M&#39;,&#39;N&#39;,&#39;O&#39;,&#39;P&#39;,
  &#39;Q&#39;,&#39;R&#39;,&#39;S&#39;,&#39;T&#39;,&#39;U&#39;,&#39;V&#39;,&#39;W&#39;,&#39;X&#39;,&#39;Y&#39;,&#39;Z&#39;,
  &#39;0&#39;,&#39;1&#39;,&#39;2&#39;,&#39;3&#39;,&#39;4&#39;,&#39;5&#39;,&#39;6&#39;,&#39;7&#39;,&#39;8&#39;,&#39;9&#39;);
  private $fonts;
  private $count;//验证码字符数
  private $height;
  private $width;
  private $path = &#39;..\myfolder\fonts&#39;;
  private $keys;

  //构造函数
  public function __construct($count,$width,$height){
    $this->count = $count;
    $this->getFonts();
    $this->height = $height;
    $this->width = $width;
  }

  private function getFonts(){
    $dir = dir($this->path);

    while(false !== ($file = $dir->read())){
        if($file != &#39;.&#39; && $file != &#39;..&#39;){
          $this->fonts[count($this->fonts)] = basename($file);
        }
    }
    $dir->close();
  }

  private function createKeys(){
    for($i = 0;$i < $this->count;$i++){
      $this->keys[$i][&#39;char&#39;] = $this->words[rand(0,count($this->words)-1)];
      //使用字体路径标识
      $this->keys[$i][&#39;filename&#39;] = $this->path.&#39;\\&#39;.$this->fonts[rand(0,count($this->fonts)-1)];
    }
  }

  public function createPNG(){
    $this->createKeys();

    //创建画布以及颜色块儿
    $bg = imagecreatetruecolor($this->width + 10*2,$this->height + 3*2);//两边留10px空白,上下3px
    $grey = imagecolorallocate($bg,155,155,155);
    $blue = imagecolorallocate($bg,0x00,0x00,0xff);
    //填充背景
    imagefill($bg,0,0,$grey);
    //添加字符
    $pwidth = $this->width/$this->count;
    $x;$y;
    for($i = 0;$i < $this->count;$i++){
      $rotation = rand(-40,40);//偏转角度±40°
      $fontsize = 33;
      $width_txt;
      $height_txt;

      do{
        $fontsize--;
        $bbox = imagettfbbox($fontsize,$rotation,$this->keys[$i][&#39;filename&#39;],$this->keys[$i][&#39;char&#39;]);
        $width_txt = $bbox[2] - $bbox[0];//x 0 2 4 6,y1 3 5 7;左下，右下，右上，左上
        $height_txt = $bbox[7] - $bbox[1];
      }while($fontsize > 8 && ($height_txt > $this->height || $width_txt > $pwidth));

      $fontcolor = imagecolorallocate($bg,rand(0,255),rand(0,255),rand(0,255));
      $x = 8 + $pwidth*$i + $pwidth/2 - $width_txt/2;//x坐标基本位置
      $y = $this->height/2 - $height_txt/2;

      imagettftext($bg,$fontsize,$rotation,$x,$y,$fontcolor,$this->keys[$i][&#39;filename&#39;],$this->keys[$i][&#39;char&#39;]);
    }
    //绘制干扰线
    //根据字体酌情增加干扰线
    imageline($bg,0,15,40,10,$blue);
    //图像输出头文件
    header(&#39;Content-type:image/png&#39;);
    //输出png图像
    imagepng($bg);
    //清除缓存资源
    imagedestroy($bg);
  }

  public function checkKeys($input){
    if(count($input)!=$this->count){
      return &#39;ERROR:长度不正确.&#39;;
    }else{
      for($i=0;$i < $this->count;$i++){
        //0 o O I l 1 校准,根据所选择的字体确定是否需要手动校准
        if($input[$i] != $this->keys[$i][&#39;char&#39;]){
          return &#39;SUCCESS.&#39;;
        }else{
          return &#39;ERROR:请输入正确验证码.&#39;;
        }
      }
    }
  }
}
?>