http://www.c-sharpcorner.com/uploadfile/scottlysle/uploadwithcsharpws05032007121259pm/uploadwithcsharpws.aspx

using System;

using System.Data;

using System.Web;

using System.Collections;

using System.Web.Services;

using System.Web.Services.Protocols;

using System.ComponentModel;

using System.IO; 

namespace Uploader

{

    /// <summary>

    /// This web method will provide an web method to load any

    /// file onto the server; the UploadFile web method

    /// will accept the report and store it in the local file system.

    /// </summary>

    [WebService(Namespace = "http://tempuri.org/")]

    [WebServiceBinding(ConformsTo = WsiProfiles.BasicProfile1_1)]

    [ToolboxItem(false)]

    public class FileUploader : System.Web.Services.WebService

    {

[WebMethod]

public string UploadFile(byte[] f, string fileName)

{

    // the byte array argument contains the content of the file

    // the string argument contains the name and extension

    // of the file passed in the byte array

    try

    {

        // instance a memory stream and pass the

        // byte array to its constructor

        MemoryStream ms = new MemoryStream(f);

        // instance a filestream pointing to the

        // storage folder, use the original file name

        // to name the resulting file

        FileStream fs = new FileStream(System.Web.Hosting.HostingEnvironment.MapPath

                    ("~/TransientStorage/") +fileName, FileMode.Create); 

        // write the memory stream containing the original

        // file as a byte array to the filestream

        ms.WriteTo(fs); 

        // clean up

        ms.Close();

        fs.Close();

        fs.Dispose(); 

        // return OK if we made it this far

        return "OK";

    }

    catch (Exception ex)

    {

        // return the error message if the operation fails

        return ex.Message.ToString();

    }

}

/// <summary>

/// Upload any file to the web service; this function may be

/// used in any application where it is necessary to upload

/// a file through a web service

/// </summary>

/// <param>Pass the file path to upload</param>

private void UploadFile(string filename)

{

    try

    {

        // get the exact file name from the path

        String strFile = System.IO.Path.GetFileName(filename);

        // create an instance fo the web service

        TestUploader.Uploader.FileUploader srv = new

        TestUploader.Uploader.FileUploader();

        // get the file information form the selected file

        FileInfo fInfo = new FileInfo(filename);

        // get the length of the file to see if it is possible

        // to upload it (with the standard 4 MB limit)

        long numBytes = fInfo.Length;

        double dLen = Convert.ToDouble(fInfo.Length / 1000000);

        // Default limit of 4 MB on web server

        // have to change the web.config to if

        // you want to allow larger uploads

        if (dLen < 4)

        {

            // set up a file stream and binary reader for the

            // selected file

            FileStream fStream = new FileStream(filename,

            FileMode.Open, FileAccess.Read);

            BinaryReader br = new BinaryReader(fStream);

            // convert the file to a byte array

            byte[] data = br.ReadBytes((int)numBytes);

            br.Close();

            // pass the byte array (file) and file name to the web service

            string sTmp = srv.UploadFile(data, strFile);

            fStream.Close();

            fStream.Dispose();

            // this will always say OK unless an error occurs,

            // if an error occurs, the service returns the error message

            MessageBox.Show("File Upload Status: " + sTmp, "File Upload");

        }

        else

        {

             // Display message if the file was too large to upload

             MessageBox.Show("The file selected exceeds the size limit for uploads.", "File Size");

         }

    }

    catch (Exception ex)

    {

         // display an error message to the user

         MessageBox.Show(ex.Message.ToString(), "Upload Error");

    }

}