以下为引用的内容：

<?
/**
  * 图象水印库类，目前支持jpg,gif,png,wbmp四种图象格式，支持图象和文字水印两种模式
  * 能左右设定水印的位置等
  * @author:feifengxlq <许立强feifengxlq#gmail.com>
  * @since:2006-10-21
  * @version:0.1
  * @copyright:http://www.phpobject.net
  *-------------------------使用实例----------------------------------------------
  * 图象水印：
  * demo 1:主要用于测试，输出水印图片
  * require_once('../libs/classes/Watermark.class.php');
  * $watermark=new watermark('../src/images/photo.jpg');
  * $watermark->set('is_output',true);
  * $watermark->markpic('../src/images/source.gif');
  * demo 2:水印目标图片
  * require_once('../libs/classes/Watermark.class.php');
  * $watermark=new watermark('../src/images/photo.jpg');
  * $watermark->markpic('../src/images/source.gif');//直接在原图象上水印
*/
class Watermark{
   
   var $gdinfo;//当前GD库的信息
   
   var $picpath;//需要水印的图片的路径
   
   var $picinfo;//水印图片的信息
   
   var $min_width=100;//需要加水印图片的最小宽度
   
   var $min_height=30;//最小高度
   
   var $mark_border=10;//水印边距
   
   var $mark_pct=60;//水印透明度
   
   var $errormsg='';//出错信息
   
   var $mark_style=5;//水印位置 0：随即 1：左上 2：右上 3：中间 4：左下 5：右下
   
   var $is_output=false;//是否输出图象
   
   var $image_output_method='imagejpeg';//输出图象的函数
   
   function __construct($picpath){
      //检查是否支持GD库
      $this->check_gd();
      $this->picinfo=$this->get_pic_info($picpath);
      $this->picpath=$picpath;
      $this->is_necessary();//检查是否需要加水印
   }  
   
   /**
     *使用图片来显示水印
     *@param:$picinfo
     *@return :
   */
   function markpic($picpath,$newpicpath='',$style=0){
      if(empty($style))$style=$this->mark_style;
      $picim=$this->image_create($this->picinfo);
      //获取水印图片的信息
      $waterpic=$this->get_pic_info($picpath);
      //检查是否适合水印
      if(($waterpic['width']+2*$this->mark_border>$this->picinfo['width'])||($waterpic['height']+2*$this->mark_border>$this->picinfo['height'])){
         $this->error(4);
      }
      $waterim=$this->image_create($waterpic);
      //水印合并图片
      $picim=$this->imagemerge($picim,$waterim,$waterpic['width'],$waterpic['height'],$style);
      //输出图象
      $this->output($picim,$newpicpath);
   }
   /**
     *使用文字来显示水印(只显示英文)
     *@param:$string
     *@return :
   */
   function markstring_en($string,$newpicpath='',$style=0)
   {
      //todo      
   }
   /**
     *设置对象的属性
     *@param:$key $value
     *@return 
   */
   function set($key,$value){
      if(array_key_exists($key,get_object_vars($this))){
         $this->$key=$value;      
      }
      return false;
   }
   /**
     *获取出错信息
     *@param void
     *@return 
   */
   function get_error(){
      return $this->errormsg;
   }
/*----------------------以下为私有方法-------------------------------------------------*/
   /**
     *输出图象
     *@param:....
     *@return 
   */
   function output($picim,$newpicpath='')
   {
      $method_name=$this->image_output_method;
      if($this->is_output){
        header('Content-type: '.$this->picinfo['mime']);
        $method_name($picim);
      }else{
        if(empty($newpicpath)){
           $newpicpath=$this->picinfo['path'];
           @unlink($this->picinfo['path']);
        }
        //写入新的文件
        if(!@$method_name($picim,$newpicpath))$this->error(5);
        return true;
      }
   }
   /**
     *合并水印图象
     *@param:....
     *@return 
   */
   function imagemerge($picim,$waterim,$water_width,$water_height,$style=5)
   {
      switch($style)
      {
         case 0:
            //随即
            $position[0]=rand($this->mark_border,$this->picinfo['width']-$this->mark_border-$water_width);//x
            $position[1]=rand($this->mark_border,$this->picinfo['height']-$this->mark_border-$water_height);//y
            break;
         case 1:
            //左上
            $position[0]=$this->mark_border;
            $position[1]=$this->mark_border;
            break;
         case 2:
            //右上
            $position[0]=$this->picinfo['width']-$this->mark_border-$water_width;
            $position[1]=$this->mark_border;
            break;    
         case 3:
            //居中
            $position[0]=round(($this->picinfo['width']-$water_width)/2);
            $position[1]=round(($this->picinfo['height']-$water_height)/2);
            break;
         case 4:
            //左下
            $position[0]=$this->mark_border;
            $position[1]=$this->picinfo['height']-$this->mark_border-$water_height;
            break;
         default:
            //右下
            $position[0]=$this->picinfo['width']-$this->mark_border-$water_width;
            $position[1]=$this->picinfo['height']-$this->mark_border-$water_height;
            break;
      }
      imagecopymerge($picim,$waterim,$position[0],$position[1],0,0,$water_width,$water_height,$this->mark_pct);
      return $picim;
   }
   
   /**
     *检查系统环境是否支持GD库
     *return:
   */
   function check_gd(){
      if(!extension_loaded('gd'))$this->error(0);
      $this->gdinfo=gd_info();
   }
   /**
     *新建一个基于调色板的图像
     *@param:$picinfo
     *@return :$im 图象标识符
   */
   function image_create($picinfo='')
   {
      if(empty($picinfo))$picinfo=$this->picinfo;
      //echo $picinfo['mime'];
      switch(trim($picinfo['mime']))
      {
         case 'image/gif':
            $this->image_output_method='imagegif';//获取输出图象的方法名称
            return imagecreatefromgif($picinfo['path']);
            break;
         case 'image/jpeg':
            $this->image_output_method='imagejpeg';
            return imagecreatefromjpeg($picinfo['path']);
            break;
         case 'image/png':
            $this->image_output_method='imagepng';
            return imagecreatefrompng($picinfo['path']);
            break;
         case 'image/wbmp':
            $this->image_output_method='imagewbmp';
            return imagecreatefromwbmp($picinfo['path']);
            break;
        default:
            $this->error(3);
            break;
      }
   }
   /**
     *获取图片的信息，主要是高度，宽度、类型
     *@param:$path:文件路径
     *@return :$picinfo array
   */
   function get_pic_info($path)
   {
      if(!file_exists($path))$this->error(1,$path);
      $info=getimagesize($path);
      if(empty($info))$this->error(1,$path);      
      $picinfo['width']=$info[0];
      $picinfo['height']=$info[1];
      $picinfo['mime']=$info['mime'];
      $picinfo['path']=$path;
      return $picinfo;      
   }
   /**
     *检查图片是否需要加水印
     *@param $picinfo图片信息
     *@return boolean
   */
   function is_necessary($picinfo=''){
      if(empty($picinfo))$picinfo=$this->picinfo;
      if(!is_array($picinfo))$this->error(2);
      if(($picinfo['width']<$this->min_width)||($picinfo['height']<$this->min_height)){
         $this->error(4);
      }
      return true;
   }
   /**
    *出错处理
   */
   function error($id,$other=''){
      switch($id){
         case '0':
            $errormsg='你的服务器不支持GD库！';
            break;
         case '1':
            $errormsg='不是有效的图片！';
            break;
         case '2':
            $errormsg='出错：函数is_necessary()中的参数必须是数组！';
            break;
         case '3':
            $errormsg='出错：目前水印只支持gif,jpg,png,wbmp四种格式的图片！';
            break;
         case '4':
            $errormsg='图片太小，不适合水印！';
            break;
         default:
            $errormsg='出错了，原因未知！';
            break;
      }
      die($errormsg.$other);
   }
}
?>