The type or namespace name 'Bytescout' could not be found (are you missing a using directive or an assembly reference?)

using System;
using System.Data;
using System.Configuration;
using System.Collections;
using System.Drawing.Imaging;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Web.UI.HtmlControls;
using System.Drawing;
using System.Collections.Generic;

using Bytescout.BarCodeReader;

namespace WebTestSharp
{
    public partial class _Default : System.Web.UI.Page
    {
        protected void UploadButton_Click(object sender, EventArgs e)
        {
            String savePath = @"\uploads\";

            if (FileUpload1.HasFile)
            {
                String fileName = FileUpload1.FileName;
                savePath += fileName;
                FileUpload1.SaveAs(Server.MapPath(savePath));

                Reader barcodeReader = new Reader();

                // reader.MediumTrustLevelCompatible = true; // uncomment this line to enable Medium Trust compatible mode (slows down the recognition process as direct image data access is disabled in Medium Trust mode)
                UploadStatusLabel.Visible = false;

                ListBox1.Items.Clear();
                ListBox1.Visible = true;
                ListBox1.Items.Add("Reading barcode(s) from image #" + imgNum);

                FoundBarcode[] barcodes = barcodeReader.ReadFrom(savePath);

                if (barcodes.Length == 0)
                {
                    ListBox1.Items.Add("    No barcodes found");
                }
                else
                {
                    foreach (FoundBarcode barcode in barcodes)
                        ListBox1.Items.Add(String.Format("Found barcode with type '{0}' and value '{1}'", barcode.Type, barcode.Value));
                }

            }
            else
            {
                // Notify the user that a file was not uploaded.
                UploadStatusLabel.Text = "You did not specify a file to upload.";
            }
        }
    }
}