Update Image

Still no result,
I added $config['overwrite']    = false; as @kenjis say but still the first image is displayed even after the replace
if ($_FILES['image_thumb']['name']) {
                        $config['upload_path'] = './uploads/product_image/';
                        $config['allowed_types'] = 'gif|jpg|png|jpeg|JPEG|GIF|JPG|PNG';
                        $config['max_size'] = "1024";
                        $config['max_width'] = "*";
                        $config['max_height'] = "*";
                        $config['encrypt_name'] = TRUE;
                        $config['overwrite']    = false;