如何检查水印是否适用？

Question

我正在尝试在文件夹中对我的所有图像应用水印。为了得到工作，我正在使用这行代码。

<?php

  function endsWith($currentString, $target)
  {
    $length = strlen($target);
     if ($length == 0) {
      return true;
    }

  return (substr($currentString, -$length) === $target);
 }
  if ($handle = opendir('images')) {
 while (false !== ($entry = readdir($handle))) {
    if ($entry != "." && $entry != "..") {

        if (endsWith($entry,'.jpg')==0){
          echo   "<br/> $entry: is ignored.\n  ";
          continue;
        }
         echo "<br/> $entry\n  ";
   $image_path = "images/".$entry; 
   $watermark = imagecreatefrompng('wa/ap.png');   
  $watermark_width = imagesx($watermark);
  $watermark_height = imagesy($watermark);  
  $image = imagecreatefromjpeg($image_path);
  if ($image === false) {
     return false;
    }
   $tragetedImageSize = getImageSize($image_path);
  $wmPositionX = $tragetedImageSize[0]- $watermark_width - 6;
  $wmPositionY = $tragetedImageSize[1] - $watermark_height - 6;
   imagealphablending($image, true);
   imagealphablending($watermark, true);
   imagecopy($image, $watermark, $wmPositionX, $wmPositionY, 0, 0, $watermark_width, $watermark_height);
   imagejpeg($image, "images/$entry");
   imagedestroy($image);
   imagedestroy($watermark);

     }
    }
    closedir($handle);
   }
 ?>

这段代码工作正常。但是现在如果在这个文件夹中添加一个新图像并再次运行我的PHP代码，那么上一次alredy水印的其他图像。我想跳过那些上次加水印的图像。

Extra ::如果images文件夹中有更多子文件夹，那么还需要更改哪些代码？

由于