Image and no image

Hello,
I have this set up to upload an image and if any of the fields are empty you get a "All fields required". Now I can't figure out how to post the upload with or without an image. This is the code I have so far: I want to thank everybody so very much for all of your help!!!!!

if (isset($_POST['submit']))
{
//Grab user data
$id=mysqli_real_escape_string($dbc, trim($_POST['id']));
$user_name=$_POST['user_name'];
$image=mysqli_real_escape_string($dbc, trim($_FILES['image']['name']));
$image_type=mysqli_real_escape_string($dbc, trim($_FILES['image']['type']));
$image_size=mysqli_real_escape_string($dbc, trim($_FILES['image']['size']));
$bookname=strip_tags(trim($_POST['bookname']));
$song1=strip_tags(trim($_POST['song1']));
$song2=strip_tags(trim($_POST['song2']));
$booklink=mysqli_real_escape_string($dbc, trim($_POST['booklink']));

if (!empty($user_name) && !empty($image) && !empty($bookname) && !empty($song1) && !empty($song2) && !empty($booklink))
{
      if ((($image_type == 'image/gif') || ($image_type == 'image/jpeg') || ($image_type == 'image/pjpeg'))
        && ($image_size > 0) && ($image_size <= JGT_MAXFILESIZE))
        {
        if ($_FILES['image']['error'] == 0)
        {
          // Move the file to the target upload folder
          $target = JGT_UPLOADPATH . $image;
          if (move_uploaded_file($_FILES['image']['tmp_name'], $target))
          {


$dbc=mysqli_connect(DB_HOST,DB_USER,DB_PASSWORD,DB_NAME)
or die('Error connecting to the server');
$query="INSERT INTO tabs (user_name, image, bookname, song1, song2, booklink) VALUES ('$user_name', '$image', '$bookname', '$song1', '$song2', '$booklink')";
mysqli_query($dbc,$query)
or die('Error querying database.');