/**
 * 生成水印
 *
 * @param 
 * @author 编程之家 jb51.cc jb51.cc
 **/
 public function water($source,$water,$alpha=60){
  if(!file_exists($source) && !file_exists($water)){
   return false;
  }
  $sInfo = $this->getImageInfo($source);
  $wInfo = $this->getImageInfo($water);
  $sType = $sInfo['type'];
  $wType = $wInfo['type'];
  $sFun  = "imagecreatefrom".$sType;
  $sImage= $sFun($source);
  $wFun  = "imagecreatefrom".$wType;
  $wImage= $wFun($water);
  imagealphablending($wImage,true);
  //图像位置,默认为右下角右对齐
  $posX =$sInfo['width'] - $wInfo['width'];
  $posY =$sInfo['height'] - $wInfo['height']; 
  imagecopymerge($sImage,$wImage,$posX,$posY,$wInfo['width'],$wInfo['height'],$alpha);
  $ImageFun = 'Image' . $sInfo['type'];
  $ImageFun($sImage);
  imagedestroy($sImage);
  imagedestroy($wImage);
 }