string url = "http://someServerApp.aspx";
            
            FileStream fs = File.Open(@"d:\a.jpg", FileMode.Open, FileAccess.Read);
            byte[] data = new byte[fs.Length];
            fs.Read(data, 0, data.Length);
            fs.Close();

            Dictionary<string, object> postParam = new Dictionary<string, object>();
            postParam.Add("1stParam", "1stValue");
            postParam.Add("2ndParam", "2ndValue");
            postParam.Add("file", new MultiPartUpload.FileParameter(data , "abc.jpg" , "image/jpeg"));

            HttpWebResponse webResponse = MultiPartUpload.MultipartFormDataPost(url, "", postParam);
            StreamReader reader = new StreamReader(webResponse.GetResponseStream());
            TraceBox.trace(reader.ReadToEnd());

            webResponse.Close();

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Xml.Linq;
using System.IO;
namespace SimpleRequest
{
    public partial class test : System.Web.UI.Page
    {
        protected void Page_Load(object sender, EventArgs e)
        {
            print("post count : " + this.Request.Form.Count + Environment.NewLine);
            foreach (string str in Request.Form)
            {
                print("name : " + str + "     value : " + Request.Form[str]);
            }

            print("FileCount : " + Request.Files.Count);
            if (Request.Files.Count == 0)
                return;

            HttpPostedFile file = Request.Files[0];
            print("-- fileName : " + file.FileName);
            print("-- fileSize : " + file.InputStream.Length);
        }

        private void print(object str)
        {
            Response.Write(str.ToString() + Environment.NewLine);
        }
    }
}