//this is the code you have to use in you controller
$config['upload_path'] = './uploads/';
// directory (http://localhost/codeigniter/index.php/your directory)
$config['allowed_types'] = 'gif|jpg|png|jpeg';
//Image type
$config['max_size'] = 0;
// I have chosen max size no limit
$new_name = time() . '-' . $_FILES["txt_file"]['name'];
//Added time function in image name for no duplicate image
$config['file_name'] = $new_name;
//Stored the new name into $config['file_name']
$this->load->library('upload', $config);
if (!$this->upload->do_upload() && !empty($_FILES['txt_file']['name'])) {
$error = array('error' => $this->upload->display_errors());
$this->load->view('production/create_images', $error);
} else {
$upload_data = $this->upload->data();
}