$images = ['1.jpg', '4.jpg'];
$directory = './images/';

function deleteUnwantedImages($images, $directory) {
  $scanned_directory = array_diff(scandir($directory), array('..', '.'));

  foreach ($scanned_directory as $key => $value) {
    if(!in_array($value, $images)) {
      unlink($directory . $value);
    }
  }
} // 2.jpg and 3.jpg will be deleted