PHP实现的给图片添加水印功能，可添加文字水印或图片水印，使用文字水印时需要提供字体文件，使用图片水印时需要提供水印图片，水印图片不能比要添加水印的图片大，请使用背景透明的水印图片。

该水印类支持自定义水印位置、自定义水印大小和水印的透明度，字体水印可自定义颜色等，功能已相应完善。

完整源代码如下(注解中已给出使用示例)：

<?php
/**
 * 图片加水印类，支持文字水印、透明度设置、自定义水印位置等。
 * 使用示例：
 *      $obj = new WaterMask($imgFileName);				//实例化对象
 *      $obj->$waterType = 1;						//类型：0为文字水印、1为图片水印
 *      $obj->$transparent = 45;					//水印透明度
 *      $obj->$waterStr = 'www.codetc.com';				//水印文字
 *      $obj->$fontSize = 18;						//文字字体大小
 *      $obj->$fontColor = array(255,255,255);				//水印文字颜色（RGB）
 *      $obj->$fontFile = 'AHGBold.ttf';				//字体文件
 *		……
 *      $obj->output();							//输出水印图片文件覆盖到输入的图片文件
 */
class WaterMask{
    public  $waterType          = 0;					//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.codetc.com';			//水印文字
    public  $fontSize           = 18;					//文字字体大小
    public  $fontColor          = array(255,255,255);			//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];
                $this->y = $this->srcImg_info[1]-$this->waterImg_info[1];
                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);
    }
}
?>