ASP.NET

public static Size GetImageDimension(string absolutePath)
    {
        byte[] imageData = File.ReadAllBytes(absolutePath);

        var fullSizeImageHeight = -1;
        var fullSizeImageWidth = -1;
        MemoryStream origStream = null;
        System.Drawing.Image fullSizeImg;
        try
        {
            origStream = new MemoryStream(imageData);
            fullSizeImg = System.Drawing.Image.FromStream(origStream);
            fullSizeImageHeight = fullSizeImg.Height;
            fullSizeImageWidth = fullSizeImg.Width;
        }
        catch
        {
        }
        finally
        {
            if (origStream != null)
                origStream.Dispose();
        }

        return new Size(fullSizeImageWidth, fullSizeImageHeight);
    }

function SimpleCallback() {
   var lCurrentStatus = PageMethods.GetCurrentStatus(ProcessResults);
}

function ProcessResults(pCurrentStatus) {
   if (pCurrentStatus != "Completed") {
       window.setTimeout("SimpleCallback()", 100);
   }
}

function SaveButtonClick(pArgument) {
   var lAjaxManager = $find("<%= MyAjaxManager.ClientId %>");
   lAjaxManager.ajaxRequest(pArgument);
   SimpleCallback();
}

<asp:Button ID="SaveButton" runat="server" Text="Save" OnClientClick="return SaveButtonClick('SaveStuff');"

[WebMethod]
public static string GetCurrentStatus()
{
   return FCurrentStatus;
}

protected void MyAjaxManager_AjaxRequest(object sender, AjaxRequestEventArgs e)
{
    if (e.Argument == "SaveStuff")
    {
        FCurrentStatus = "ProcessRunning";
        SaveInformation();
    }
}

//While this is being executed the webmetod, GetCurrentStatus, is ignored until this process is completed
delegate void MyLongRunningProcess();

private void SaveInformation()
{
  var lLongRunningMethod = new MyLongRunningProcess(NextClass.Save());
  
  IAsyncResult lResult = lLongRunningMethod.BeginInvoke(null, null);

  while (!lResult.IsCompleted)
  {
     //Update progressbar with new percentage
  }
 
  lLongRunningMethod.EndInvoke(lResult);
}