PHP에서 업로드된 파일 형식을 제한하는 방법

<?php
$allowedExts = array("gif", "jpeg", "jpg", "png");
$extension = end(explode(".", $_FILES["file"]["name"]));
if ((($_FILES["file"]["type"] == "image/gif")
|| ($_FILES["file"]["type"] == "image/jpeg")
|| ($_FILES["file"]["type"] == "image/jpg")
|| ($_FILES["file"]["type"] == "image/pjpeg")
|| ($_FILES["file"]["type"] == "image/x-png")
|| ($_FILES["file"]["type"] == "image/png"))
&& ($_FILES["file"]["size"] < 20000)
&& in_array($extension, $allowedExts))
 {
 if ($_FILES["file"]["error"] > 0)
  {
  echo "Return Code: " . $_FILES["file"]["error"] . "<br>";
  }
 else
  {
  echo "Upload: " . $_FILES["file"]["name"] . "<br>";
  echo "Type: " . $_FILES["file"]["type"] . "<br>";
  echo "Size: " . ($_FILES["file"]["size"] / 1024) . " kB<br>";
  echo "Temp file: " . $_FILES["file"]["tmp_name"] . "<br>";
  if (file_exists("upload/" . $_FILES["file"]["name"]))
   {
   echo $_FILES["file"]["name"] . " already exists. ";
   }
  else
   {
   move_uploaded_file($_FILES["file"]["tmp_name"],
   "upload/" . $_FILES["file"]["name"]);
   echo "Stored in: " . "upload/" . $_FILES["file"]["name"];
   }
  }
 }
else
 {
 echo "Invalid file";
 }
?>