CTUploadCheckout.php

<?php

public function cartthrob_pre_process($options)
{
    if (isset($_FILES)) {
        // load the libraries and models
        ee()->load->model('file_upload_preferences_model');

        // get upload preferences
        $uploadPrefs = ee()->file_upload_preferences_model->get_file_upload_preferences(null, 2);

        $config = array(
            'upload_path'       => $uploadPrefs['server_path'],
            'allowed_types'     => '*',
            'max_size'          => $uploadPrefs['max_height'],
            'max_width'         => $uploadPrefs['max_width'],
            'max_height'        => $uploadPrefs['max_height'],
            'overwrite'         => FALSE, // default
            'remove_spaces'     => TRUE, // default
        );

        ee()->load->library('upload', $config);

        if (ee()->upload->do_upload('order_po_upload'))
        {
            // Create thumbnail
            ee()->load->library('filemanager');
            ee()->load->model('file_model');
            ee()->filemanager->create_thumb($uploadPrefs['server_path'] . ee()->upload->file_name, array(
                'file_name' => ee()->upload->file_name,
                'dimensions' => null,
                'server_path' => $uploadPrefs['server_path']
            ));

            // Save File
            ee()->file_model->save_file(array(
                'site_id'               => ee()->config->item('site_id'),
                'title'                 => ee()->upload->file_name,
                'upload_location_id'    => 2,
                'rel_path'              => ee()->upload->upload_path,
                'mime_type'             => ee()->upload->file_type,
                'file_name'             => ee()->upload->file_name,
                'file_size'             => ee()->upload->file_size,
                'uploaded_by_member_id' => ee()->session->userdata['member_id'],
                'upload_date'           => ee()->localize->now
            ));
        }

        $_POST['order_po_upload'] = '{filedir_2}' . ee()->upload->file_name;
    }
}