What is the difference between $_FILES["file"]["type"] and end(explode(".", $_FILES["file"]["name"]))

If you want to be sure that an image was uploaded, use getimagesize, that returns 0 for non-images.

You're absolutely correct. The MIME type is provided by the client and you cannot guarantee it is cor­rect. For that matter, so is the file extension. If you need to be completely sure, you need to look at the file contents.