<%@ WebHandler Language="C#" Class="index" %>

using System;
using System.Web;
using ZXing;
using ZXing.Common;
using System.Drawing;
using System.Drawing.Imaging;

public class index : IHttpHandler
{

    public void ProcessRequest(HttpContext context)
    {
        context.Response.ContentType = "text/plain";

        EncodingOptions eo = new EncodingOptions();
        eo.Width = 400;
        eo.Height = 100;
        eo.Margin = 2;

        BarcodeWriter bw = new BarcodeWriter();
        bw.Options = eo;
        bw.Format = BarcodeFormat.CODE_128;
        Bitmap bm = bw.Write(context.Request["barcode"] is object ? context.Request["barcode"].ToString() : "12345678901");
        //bm.Save(context.Server.MapPath("barcode.jpg"), ImageFormat.Jpeg);

        HttpResponse Response = context.Response;
        Response.ClearContent();
        Response.ContentType = "image/jpeg";
        bm.Save(Response.OutputStream, ImageFormat.Jpeg);
        bm.Dispose();
    }

    public bool IsReusable
    {
        get
        {
            return false;
        }
    }

}