Assistance with if..elseif statement

I have this block of code which checks to see if an image has been uploaded from an update form. Everything in the form works, except I can not get the the elseif statements to behave properly. See the comments below for explanation. Any help would be appreciated. $route_photo = $_FILES['image']['name']; // if no new image and no existing image put NULL in the DB if(empty($_FILES['image']['name']) && ($_POST['oldimage']) == '')

        {
            $route_photo = 'NULL';
             echo ("No image supplied.");

// if new image put the new image name in the DB

        }  elseif ($_POST['route_photo'] || $_FILES['image']['name']) {
              $route_photo = $_POST['route_photo'];
                 echo ("The image has been replaced with $route_photo.");

// If no new image update, use the old image

        }  elseif ($_POST['route_photo'] = $_POST['oldimage'])
                    {
                     $route_photo = $_POST['oldimage'];
                        echo("No new image supplied");
                    }