php简单验证码
    <!--  网站建设www.ucantech.com
    *@copyright(c)2011 
    *@author:Ernest 
    *@time:2011 
    *@version:new 
    --> 
     
    <?php 
     
    class VerifyImg { 
        public $fontSize = 15; //定义字体大小 
        public $length = 4; //定义字符串长度                         
        public $width = 70; //定义图片宽度 
        public $height = 30; //定义图片高度 
        public $im = null; //生成一张指定宽高的图片 
        public $font = 'C:/Windows/Fonts/Arial.TTF'; 
        public $strNum = ""; 
        public function Build() { 
            $strings = Array ('1', '2','3', '4', '5', '6', '7', 'a', 'b', 'c', 'd', 'e', 'f', 'h', 'i', 'j', 'k', 'm', 'n', 'p', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y' ); 
    //      $strNum = ""; 
            $count = count ( $strings ); 
            for($i = 1; $i <= $this->length; $i ++) { //循环随机取字符生成字符串 
                $strNum .= $strings [rand ( 0, $count - 1 )]; 
            } 
            session_start (); 
            $_SESSION ["verifycode"] = $strNum; 
            $this->im = imagecreate ( $this->width, $this->height ); 
            $backgroundcolor = imagecolorallocate ( $this->im, 255, 255, 255 ); //生成背景色 
            $frameColor = imageColorAllocate ( $this->im, 0, 255, 0 ); 
            for($i = 0; $i < $this->length; $i ++) { 
                $charY = ($this->height + 9) / 2 + rand ( - 1, 1 ); //定义字符Y坐标 
                $charX = $i * 15 + 8; //定义字符X坐标 
                //            $text_color = imagecolorallocate($this->im, 255, 0, 0);                                                //生成字符颜色 
                $text_color = imagecolorallocate ( $this->im, mt_rand ( 50, 255 ), mt_rand ( 50, 128 ), mt_rand ( 50, 200 ) ); 
              &nb