//驗證碼寬度
private $width;
//驗證碼高度
private $height;
//驗證的個數
private $length;
//干擾點個數
private $dots;
//干擾點的類型
private $type;
//干擾線個數
private $lines;
//文字
private $font;

?php
//創建驗證碼工具類
class captcha {
 //驗證碼的各種參數
 //驗證碼寬度
 private $width;
 //驗證碼高度
 private $height;
 //驗證的個數
 private $length;
 //干擾點個數
 private $dots;
 //干擾點的類型
 private $type;
 //干擾線個數
 private $lines;
 //文字
 private $font;
 //驗證碼屬性的構造方法
 public function __construct($arr = array ()) {
  //將屬性賦值
  $this->width = isset ($arr['width']) ? trim($arr['width']) : '270';
  $this->height = isset ($arr['height']) ? trim($arr['height']) : '30';
  $this->length = isset ($arr['length']) ? trim($arr['length']) : '4';
  $this->dots = isset ($arr['dots']) ? trim($arr['dots']) : '81';
  $this->type = isset ($arr['type']) ? trim($arr['type']) : '*';
  $this->lines = isset ($arr['lines']) ? trim($arr['lines']) : '5';
  $this->font = isset ($arr['font']) ? trim($arr['font']) : './cambriab.ttf';
 }
 //創建驗證碼的方法
 public function captcha() {
  //創建畫布
  $img = imagecreatetruecolor($this->width, $this->height);
  //填充顏色
  //顏色資源
  $color = imagecolorallocate($img, mt_rand(200, 255), mt_rand(200, 255), mt_rand(200, 255));
  //填充背景
  imagefill($img, 0, 0, $color);
  //添加干擾點
  for ($i = 0; $i  $this->dots; $i++) {
   //顏色資源
   $dots_color = imagecolorallocate($img, mt_rand(150, 200), mt_rand(150, 200), mt_rand(150, 200));
   //插入干擾點
   imagestring($img, mt_rand(1, 5), mt_rand(0, $this->width), mt_rand(0, $this->height), $this->type, $dots_color);
  }
  //添加干擾線
  for ($i = 0; $i  $this->lines; $i++) {
   //顏色資源
   $line_color = imagecolorallocate($img, mt_rand(150, 200), mt_rand(150, 200), mt_rand(150, 200));
   //插入干擾線
   imageline($img, mt_rand(0, $this->width), mt_rand(0, $this->height), mt_rand(0, $this->width), mt_rand(0, $this->height), $line_color);
  }
  //首先獲取驗證碼，然后插入驗證文字
  //文字高度
  $size = mt_rand(18, 20);
  //獲取驗證碼
  $str = $this->captchastring();
  for ($i = 0; $i  strlen($str); $i++) {
   //顏色資源
   $str_color = imagecolorallocate($img, mt_rand(50, 150), mt_rand(50, 150), mt_rand(50, 150));
   //插入驗證碼
   imagettftext($img, $size, mt_rand(-45, 45), $this->width / ($this->length + 2) * ($i +1), (($this->height - $size) / 2) + $size, $str_color, $this->font, $str[$i]);
  }
  //將得到的驗證碼存入SESSION中，便于以后的驗證碼判斷
  @ session_start();
  $_SESSION['captcha'] = $str;
  //輸出圖片
  header("content-type:image/png");
  imagepng($img);
  //清除資源
  imagedestroy($img);
 }
 //獲取隨機的驗證內容:A-Z,a-z,1-9
 private function captchaString() {
  //獲取四個隨機的字符串
  $str = "";
  for ($i = 0; $i  $this->length; $i++) {
   switch (mt_rand(1, 3)) {
    case 1 :
     $str .= chr(mt_rand(49, 57));
     break;
    case 2 :
     $str .= chr(mt_rand(97, 122));
     break;
    case 3 :
     $str .= chr(mt_rand(65, 90));
     break;
   }
  }
  return $str;
 }
 //判斷驗證碼
 public static function checkCaptcha($captcha) {
  @ session_start();
  return strtoupper($captcha) === strtoupper($_SESSION['captcha']);
 }
}
//使用方法：
$img = new captcha();//這里采用默認參數
$img->captcha();
?>