如何检查水印是否适用？

Question

I am trying to apply watermark on my all image with in folder.For get working this i am using this line of code.

<?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.
  ";
          continue;
        }
         echo "<br/> $entry
  ";
   $image_path = "images/".$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);
   }
 ?>

this code working fine. But now If add a new image in this folder and again run my php code then other image which alredy watermarked last time. I want skip those image which is watermarked last time .

Extra :: One more this if images folder have more sub folder then what code need tobe changed ?

Thanks