how to upload html5 canvas image in server

Default.aspx.cs

using System;

using System.IO;

using System.Web.Script.Services;

using System.Web.Services;

[ScriptService]

public partial class _Default : System.Web.UI.Page

{

    static string path = @"F:\Dinesh\";

    [WebMethod()]

    public static void UploadImage(string imageData)

    {

        string fileNameWitPath = path + DateTime.Now.ToString().Replace("/", "-").Replace(" ", "- ").Replace(":", "") + ".png";

        using (FileStream fs = new FileStream(fileNameWitPath, FileMode.Create))

        {

            using (BinaryWriter bw = new BinaryWriter(fs))

            {

                byte[] data = Convert.FromBase64String(imageData);

                bw.Write(data);

                bw.Close();

            }

        }

    }

}

Now, drawShapes() is working and I can see the graphics in canvas when view in browser. But when I click the button to save that canvas image in folder nothing is happen. How can I save that canvas image in my folder?