---water.class.php---类库文件

<?PHP
 class WaterMask{ 
 public $waterType = 1;                //水印类型：0为文字水印、1为图片水印 
 public $pos = 0;                //水印位置 
 public $transparent = 45;               //水印透明度 
 public $waterStr = 'www.itwhy.org';  //水印文字 
 public $fontSize = 16;               //文字字体大小 
 public $fontColor = array(255,0,255); //水印文字颜色（RGB） 
 public $fontFile = 'AHGBold.ttf';    //字体文件 
 public $waterImg = 'logo.png';       //水印图片 
 private $srcImg = '';               //需要添加水印的图片 
 private $im = '';               //图片句柄 
 private $water_im = '';               //水印图片句柄 
 private $srcImg_info = '';               //图片信息 
 private $waterImg_info = '';               //水印图片信息 
 private $str_w = '';               //水印文字宽度 
 private $str_h = '';               //水印文字高度 
 private $x = '';               //水印X坐标 
 private $y = '';               //水印y坐标 
 
 function __construct($img) {        //析构函数 
 $this->srcImg = file_exists($img) ? $img : die('"'.$img.'" 源文件不存在！'); 
 } 
 private function imginfo() {                //获取需要添加水印的图片的信息，并载入图片。 
 $this->srcImg_info = getimagesize($this->srcImg); 
 switch ($this->srcImg_info[2]) { 
 case 3: 
 $this->im = imagecreatefrompng($this->srcImg); 
 break 1; 
 case 2: 
 $this->im = imagecreatefromjpeg($this->srcImg); 
 break 1; 
 case 1: 
 $this->im = imagecreatefromgif($this->srcImg); 
 break 1; 
 default: 
 die('原图片（'.$this->srcImg.'）格式不对，只支持PNG、JPEG、GIF。'); 
 } 
 } 
 private function waterimginfo() {           //获取水印图片的信息，并载入图片。 
 $this->waterImg_info = getimagesize($this->waterImg); 
 switch ($this->waterImg_info[2]) { 
 case 3: 
 $this->water_im = imagecreatefrompng($this->waterImg); 
 break 1; 
 case 2: 
 $this->water_im = imagecreatefromjpeg($this->waterImg); 
 break 1; 
 case 1: 
 $this->water_im = imagecreatefromgif($this->waterImg); 
 break 1; 
 default: 
 die('水印图片（'.$this->srcImg.'）格式不对，只支持PNG、JPEG、GIF。'); 
 } 
 } 
 private function waterpos() {               //水印位置算法 
 switch ($this->pos) { 
 case 0:     //随机位置 
 $this->x = rand(0,$this->srcImg_info[0]-$this->waterImg_info[0]); 
 $this->y = rand(0,$this->srcImg_info[1]-$this->waterImg_info[1]); 
 break 1; 
 case 1:     //上左 
 $this->x = 0; 
 $this->y = 0; 
 break 1; 
 case 2:     //上中 
 $this->x = ($this->srcImg_info[0]-$this->waterImg_info[0])/2; 
 $this->y = 0; 
 break 1; 
 case 3:     //上右 
 $this->x = $this->srcImg_info[0]-$this->waterImg_info[0]; 
 $this->y = 0; 
 break 1; 
 case 4:     //中左 
 $this->x = 0; 
 $this->y = ($this->srcImg_info[1]-$this->waterImg_info[1])/2; 
 break 1; 
 case 5:     //中中 
 $this->x = ($this->srcImg_info[0]-$this->waterImg_info[0])/2; 
 $this->y = ($this->srcImg_info[1]-$this->waterImg_info[1])/2; 
 break 1; 
 case 6:     //中右 
 $this->x = $this->srcImg_info[0]-$this->waterImg_info[0]; 
 $this->y = ($this->srcImg_info[1]-$this->waterImg_info[1])/2; 
 break 1; 
 case 7:     //下左 
 $this->x = 0; 
 $this->y = $this->srcImg_info[1]-$this->waterImg_info[1]; 
 break 1; 
 case 8:     //下中 
 $this->x = ($this->srcImg_info[0]-$this->waterImg_info[0])/2; 
 $this->y = $this->srcImg_info[1]-$this->waterImg_info[1]; 
 break 1; 
 default:    //下右 
 $this->x = $this->srcImg_info[0]-$this->waterImg_info[0]-8; 
 $this->y = $this->srcImg_info[1]-$this->waterImg_info[1]-8; 
 break 1; 
 } 
 } 
 private function waterimg() { 
 if ($this->srcImg_info[0] <= $this->waterImg_info[0] || $this->srcImg_info[1] <= $this->waterImg_info[1]){ 
 die('水印比原图大！'); 
 } 
 $this->waterpos(); 
 $cut = imagecreatetruecolor($this->waterImg_info[0],$this->waterImg_info[1]); 
 imagecopy($cut,$this->im,0,0,$this->x,$this->y,$this->waterImg_info[0],$this->waterImg_info[1]); 
 $pct = $this->transparent; 
 imagecopy($cut,$this->water_im,0,0,0,0,$this->waterImg_info[0],$this->waterImg_info[1]); 
 imagecopymerge($this->im,$cut,$this->x,$this->y,0,0,$this->waterImg_info[0],$this->waterImg_info[1],$pct); 
 } 
 private function waterstr() { 
 $rect = imagettfbbox($this->fontSize,0,$this->fontFile,$this->waterStr); 
 $w = abs($rect[2]-$rect[6]); 
 $h = abs($rect[3]-$rect[7]); 
 $fontHeight = $this->fontSize; 
 $this->water_im = imagecreatetruecolor($w, $h); 
 imagealphablending($this->water_im,false); 
 imagesavealpha($this->water_im,true); 
 $white_alpha = imagecolorallocatealpha($this->water_im,255,255,255,127); 
 imagefill($this->water_im,0,0,$white_alpha); 
 $color = imagecolorallocate($this->water_im,$this->fontColor[0],$this->fontColor[1],$this->fontColor[2]); 
 imagettftext($this->water_im,$this->fontSize,0,0,$this->fontSize,$color,$this->fontFile,$this->waterStr); 
 $this->waterImg_info = array(0=>$w,1=>$h); 
 $this->waterimg(); 
 } 
 function output() { 
 $this->imginfo(); 
 if ($this->waterType == 0) { 
 $this->waterstr(); 
 }else { 
 $this->waterimginfo(); 
 $this->waterimg(); 
 } 
 switch ($this->srcImg_info[2]) { 
 case 3: 
 imagepng($this->im,$this->srcImg); 
 break 1; 
 case 2: 
 imagejpeg($this->im,$this->srcImg); 
 break 1; 
 case 1: 
 imagegif($this->im,$this->srcImg); 
 break 1; 
 default: 
 die('添加水印失败！'); 
 break; 
 } 
 imagedestroy($this->im); 
 imagedestroy($this->water_im); 
 } 
} 
?>

---demo.php----调用示例文件

<?PHP
 include 'water.class.php';
 $obj = new WaterMask("2000.jpg");//实例化传参数需要打水印的文件或者文件地址
 $obj->waterType = 1 ;//打水印文字为0，打水印图片为1
 $obj->transparent = 100 ;//水印透明度0-100
 $obj->pos = 9;//水印位置1-无穷大 ；
/*1: 上左  2: 上中 3: 上右   4: 中左 5:  中中 6: 中右  7: 下左  8: 下中  >=9 下右
*/
 $obj->waterStr = 'www'; //水印文字内容，如果是汉字则需要字体支持
 $obj->fontSize = 16 ;//水印文字大小，该处16，即为水印为文字时文字大小为16px
 $obj->fontColor = array(255,0255);//水印文字颜色
 $obj->fontFile ='mini.ttf';  //水印为文字时的字体，可以设置放置位置 
 $obj->output(); //大水印后覆盖原始图片文件的方法

 echo '<img src="2000.jpg">';//示例方法输出打过水印的图片
?>

ps：水印为图片时即$obj->waterType =1 ，水印logo图片默认于类库文件在同一个文件夹，并且取名logo.png ；您可以修改类库文件设置放置位置。