imagePNG ...

imagepng($img, "" . str_replace('.nfo', '.png', "$uploaddir/nfo/$id.txt"));
$watermark = imagecreatefrompng('img/main/watermark.png');
$watermark_width = imagesx($watermark);
$watermark_height = imagesy($watermark);
$image = imagecreatetruecolor($watermark_width, $watermark_height);
$image = imagecreatefrompng($uploaddir . "img/" . $id . ".png");
$size = getimagesize($uploaddir . "nfo/" . $id . ".png");
$dest_x = $size[0] - $watermark_width - 5;
$dest_y = $size[1] - $watermark_height - 5;
imagecopymerge($image, $watermark, $dest_x, $dest_y, 0, 0, $watermark_width, $watermark_height, 100);
imagepng($image);
imagedestroy($image);
imagedestroy($watermark);
unlink($uploaddir . "img/" . $id . ".png");
  }