php实现给一张图片加上水印效果，

<&#63;php
/**
 * 功能：给一张图片加上水印效果
 *      $i 要加水印效果的图片
 *      $t 水印文字
 *      $size 文字大小
 *      $pos 水印的位置
 *      $color 文字的颜色
 *      $flag 是布尔值，主要用来区分是不是原图上加水印
 *      $type 如果$flag等于false 则新图上加上水印 新文件名为 原名_txt.jpg
 */
function txt($i,$t='版权所有',$size=25,$pos=5,$color='rand',$flag=true,$type='_txt'){
  $img = imagecreatefromjpeg($i);
  $w = imagesx($img);
  $h = imagesy($img);
  $font = dirname(__FILE__).'/font/ls.ttf';
  $ps = imagettfbbox($size,0,$font,$t);
  $tw = $ps[4];
  $th = abs($ps[5]);
  switch($pos){
    case 1:break;  
    case 2:break;  
    case 3:break;  
    case 4:break;  
    case 5:$x=($w-$tw)/2;$y=($h-$th)/2+$th;break;  
    case 6:break;  
    case 7:break;  
    case 8:break;  
    case 9:break;  
    default:break;
  }
  $c = getcolor($img,$color);
  imagettftext($img,$size,0,$x,$y,$c,$font,$t);
  if($flag){
    imagejpeg($img,$i); 
  }else{
    $ext = ext($i);
    $ppp = rtrim($i,'.'.$ext);
    $ppp = $ppp.$type.'.'.$ext;
    imagejpeg($img,$ppp);
  }
}
 
function getcolor($i,$c='rand',$a=50){
  $cc = '';
  switch($c){
    case 'white':$cc=imagecolorallocatealpha($i,255,255,255,$a);break;
    case 'black':$cc=imagecolorallocatealpha($i,0,0,0,$a);break;
    case 'red':$cc=imagecolorallocatealpha($i,255,0,0,$a);break;
    case 'green':$cc=imagecolorallocatealpha($i,0,255,0,$a);break;
    case 'blue':$cc=imagecolorallocatealpha($i,0,0,255,$a);break;
    case 'orange':$cc=imagecolorallocatealpha($i,0xff,0x66,0x33,$a);break;
    case 'yellow':$cc=imagecolorallocatealpha($i,255,255,0,$a);break;
    case 'rand':$cc=imagecolorallocatealpha($i,mt_rand(0,255),mt_rand(0,255),mt_rand(0,255),$a);break;
    default:
      $cs = substr($c,1);
      $ok = str_split($cs,2);
      $cc = imagecolorallocatealpha($i,hexdec($ok[0]),hexdec($ok[1]),hexdec($ok[2]),$a);
    break;   
  }
  return $cc;
}
 
 
/**
 * 功能是：返回扩展名
 */
 
function ext($f){
  $exts = explode('.',$f);
  return end($exts);
}
 
/**
 * 功能是：返回文件名，不含扩展名
 */
function name($f){
  $s = explode('/',$f);
  $fn = end($s);
  return rtrim($fn,'.'.ext($f));
}

function setWater($imgSrc,$markImg,$markText,$TextColor,$markPos,$fontType,$markType)
{

  $srcInfo = @getimagesize($imgSrc);
  $srcImg_w  = $srcInfo[0];
  $srcImg_h  = $srcInfo[1];
    
  switch ($srcInfo[2]) 
  { 
    case 1: 
      $srcim =imagecreatefromgif($imgSrc); 
      break; 
    case 2: 
      $srcim =imagecreatefromjpeg($imgSrc); 
      break; 
    case 3: 
      $srcim =imagecreatefrompng($imgSrc); 
      break; 
    default: 
      die("不支持的图片文件类型"); 
      exit; 
  }
    
  if(!strcmp($markType,"img"))
  {
    if(!file_exists($markImg) || empty($markImg))
    {
      return;
    }
      
    $markImgInfo = @getimagesize($markImg);
    $markImg_w  = $markImgInfo[0];
    $markImg_h  = $markImgInfo[1];
      
    if($srcImg_w < $markImg_w || $srcImg_h < $markImg_h)
    {
      return;
    }
      
    switch ($markImgInfo[2]) 
    { 
      case 1: 
        $markim =imagecreatefromgif($markImg); 
        break; 
      case 2: 
        $markim =imagecreatefromjpeg($markImg); 
        break; 
      case 3: 
        $markim =imagecreatefrompng($markImg); 
        break; 
      default: 
        die("不支持的水印图片文件类型"); 
        exit; 
    }
      
    $logow = $markImg_w;
    $logoh = $markImg_h;
  }
    
  if(!strcmp($markType,"text"))
  {
    $fontSize = 16;
    if(!empty($markText))
    {
      if(!file_exists($fontType))
      {
        return;
      }
    }
    else {
      return;
    }
      
    $box = @imagettfbbox($fontSize, 0, $fontType,$markText);
    $logow = max($box[2], $box[4]) - min($box[0], $box[6]);
    $logoh = max($box[1], $box[3]) - min($box[5], $box[7]);
  }
    
  if($markPos == 0)
  {
    $markPos = rand(1, 9);
  }
    
  switch($markPos)
  {
    case 1:
      $x = +5;
      $y = +5;
      break;
    case 2:
      $x = ($srcImg_w - $logow) / 2;
      $y = +5;
      break;
    case 3:
      $x = $srcImg_w - $logow - 5;
      $y = +15;
      break;
    case 4:
      $x = +5;
      $y = ($srcImg_h - $logoh) / 2;
      break;
    case 5:
      $x = ($srcImg_w - $logow) / 2;
      $y = ($srcImg_h - $logoh) / 2;
      break;
    case 6:
      $x = $srcImg_w - $logow - 5;
      $y = ($srcImg_h - $logoh) / 2;
      break;
    case 7:
      $x = +5;
      $y = $srcImg_h - $logoh - 5;
      break;
    case 8:
      $x = ($srcImg_w - $logow) / 2;
      $y = $srcImg_h - $logoh - 5;
      break;
    case 9:
      $x = $srcImg_w - $logow - 5;
      $y = $srcImg_h - $logoh -5;
      break;
    default: 
      die("此位置不支持"); 
      exit;
  }
    
  $dst_img = @imagecreatetruecolor($srcImg_w, $srcImg_h);
    
  imagecopy ( $dst_img, $srcim, 0, 0, 0, 0, $srcImg_w, $srcImg_h);
    
  if(!strcmp($markType,"img"))
  {
    imagecopy($dst_img, $markim, $x, $y, 0, 0, $logow, $logoh);
    imagedestroy($markim);
  }
    
  if(!strcmp($markType,"text"))
  {
    $rgb = explode(',', $TextColor);
      
    $color = imagecolorallocate($dst_img, $rgb[0], $rgb[1], $rgb[2]);
    imagettftext($dst_img, $fontSize, 0, $x, $y, $color, $fontType,$markText);
  }
    
  switch ($srcInfo[2]) 
  { 
    case 1:
      imagegif($dst_img, $imgSrc); 
      break; 
    case 2: 
      imagejpeg($dst_img, $imgSrc); 
      break; 
    case 3: 
      imagepng($dst_img, $imgSrc); 
      break;
    default: 
      die("不支持的水印图片文件类型"); 
      exit; 
  }
    
  imagedestroy($dst_img);
  imagedestroy($srcim);
}