php给现有的图片加文字水印代码

<?php
 class image_fu{
 private $image;
 private $img_info;
 private $img_width;
 private $img_height;
 private $img_im;
 private $img_text;
 private $img_ttf='';
 private $img_new;
 private $img_text_size;
 private $img_jd;
 function img($img='',$txt='',$ttf='',$size=12,$jiaodu=0){
if(isset($img)&&file_exists($img)){//检测图片是否存在
 $this->image =$img; 
$this->img_text=$txt;
$this->img_text_size=$size;
$this->img_jd=$jiaodu;
if(file_exists($ttf)){
$this->img_ttf=$ttf;
}else{
exit('字体文件：'.$ttf.'不存在！');
}
$this->imgyesno();
}else{
exit('图片文件:'.$img.'不存在');
}
}
 private function imgyesno(){
$this->img_info =getimagesize($this->image);
$this->img_width =$this->img_info[0];//图片宽
$this->img_height=$this->img_info[1];//图片高
//检测图片类型
switch($this->img_info[2]){
 case 1:$this->img_im = imagecreatefromgif($this->image);break; 
 case 2:$this->img_im = imagecreatefromjpeg($this->image);break; 
 case 3:$this->img_im = imagecreatefrompng($this->image);break; 
default:exit('图片格式不支持水印');
}
$this->img_text();
}
 private function img_text(){
imagealphablending($this->img_im,true);
//设定颜色
$color=imagecolorallocate($this->img_im,rand(0,255),rand(0,255),rand(0,255));
$txt_height=$this->img_text_size;
$txt_jiaodu=$this->img_jd;
$ttf_im=imagettfbbox($txt_height,$txt_jiaodu,$this->img_ttf,$this->img_text);
 $w = $ttf_im[2] - $ttf_im[6]; 
 $h = $ttf_im[3] - $ttf_im[7]; 
 //$w = $ttf_im[7]; 
 //$h = $ttf_im[8]; 
unset($ttf_im);
 $txt_y =$this->img_height-$h;
 $txt_x =$this->img_width-$w;
 //$txt_y =0;
 //$txt_x =0;
$this->img_new=@imagettftext($this->img_im,$txt_height,$txt_jiaodu,$txt_x,$txt_y,$color,$this->img_ttf,$this->img_text);
@unlink($this->image);//删除图片
switch($this->img_info[2]) {//取得背景图片的格式 
 case 1:imagegif($this->img_im,$this->image);break; 
 case 2:imagejpeg($this->img_im,$this->image);break; 
 case 3:imagepng($this->img_im,$this->image);break; 
 default: exit('水印图片失败'); 
}
}
//显示图片
 function img_show(){echo '<img src="'.$this->image.'"border="0"alt="'.$this->img_text.'"/>';}
//释放内存
 private function img_nothing(){
unset($this->img_info);
imagedestroy($this->img_im);
}
}
?>