php file upload

In the attached file I have the following code:
---------------------------
$formfile = "";
            
      if($_FILES['art_Thumb'] && $_FILES['art_Thumb']['size'] > 0){
            $uploaddir = "images/artists/thumb/";  //folder in which to put the file
            $ori_name = $_FILES[art_Thumb][name];
            $tmp_name = $_FILES[art_Thumb][tmp_name];
            $src = imagecreatefromjpeg($tmp_name);
            list($width,$height) = getimagesize($tmp_name);
            //landscape
            if ($width > $height) {
                  $pwidth = 450;
                  $newwidth = $pwidth;
                  $newheight = ($height/$width)*$pwidth;
            }
            //
            //portrait
            if ($height > $width) {
                  $pwidth = $width;
                  $newheight = 450;
                  $newwidth = ($width/$height)*$newheight;
            }
            //
            $tmp = imagecreatetruecolor($newwidth,$newheight);
            imagecopyresampled($tmp,$src,0,0,0,0,$newwidth,$newheight,$width,$height);
            $newfile = $uploaddir.$ori_name;
            imagejpeg($tmp,$newfile,100);
            chmod($newfile,0777);
      }
-------------------------

This is working firn for most xxx.jpg images but some images are just not being uploaded. The ones not being uploaded are still xxx.jpg and I cannot see what the problem is. All images are always > 1000 pixels wide

Help Help  please
frm-artgallery.php