Add Image to StringBuilder in ASP.Net using C#

 How to add image to ir.

    protected void PrintGridView(object sender, EventArgs e)
    {
      //Disable Paging if all Pages need to be Printed.
      if ((sender as Button).CommandArgument == "All")
      {
        //Disable Paging.
        gvDetails.AllowPaging = false;

        //Re-bind the GridView.
        this.BindData(string.Empty, string.Empty);

        //For Printing Header on each Page.
        gvDetails.UseAccessibleHeader = true;
        gvDetails.HeaderRow.TableSection = TableRowSection.TableHeader;
        gvDetails.FooterRow.TableSection = TableRowSection.TableFooter;
        gvDetails.Attributes["style"] = "border-collapse:separate";
        foreach (GridViewRow row in gvDetails.Rows)
        {
          if ((row.RowIndex + 1) % gvDetails.PageSize == 0 && row.RowIndex != 0)
          {
            row.Attributes["style"] = "page-break-after:always;";
          }
        }
      }
      else
      {
        //Hide the Pager.
        gvDetails.PagerSettings.Visible = false;
        this.BindData(string.Empty, string.Empty);
      }

      using (StringWriter sw = new StringWriter())
      {
        //Render GridView to HTML.
        HtmlTextWriter hw = new HtmlTextWriter(sw);
        gvDetails.RenderControl(hw);

        //Enable Paging.
        gvDetails.AllowPaging = true;
        this.BindData(string.Empty, string.Empty);

        //Remove single quotes to avoid JavaScript error.
        string gridHTML = sw.ToString().Replace(Environment.NewLine, "");
        //string gridCSS = gridStyles.InnerText.Replace("\"", "'").Replace(Environment.NewLine, "");

        //Print the GridView.
        //string script = "window.onload = function() { PrintGrid('" + gridHTML + "', '" + gridCSS + "'); }";
        string script = "window.onload = function() { PrintGrid('" + gridHTML + "', ''); }";
        ClientScript.RegisterStartupScript(this.GetType(), "GridPrint", script, true);
      }
    }

I've Above Code Copied From (ASPFORUMS) But But But

I Need To Add These Below Two Lines In The Above Code. How Can I Do That. Please Help.

string imgurl = "assets/img/5m-transparent-logo.png";
sb.Append(string.Format("<img id='SpeIma' src='{0}' style='width: 200px; height: 68px; margin-bottom:25px;' />", ResolveUrl(imgurl)));