problem with Gridview export to excel along with image

public static void PrepareGridViewForExport(Control gridView)
    {
        for (int i = 0; i < gridView.Controls.Count; i++)
        {
            //Get the control
            Control currentControl = gridView.Controls[i];
            if (currentControl is LinkButton)
            {
                gridView.Controls.Remove(currentControl);
                gridView.Controls.AddAt(i, new LiteralControl((currentControl as LinkButton).Text));
            }
            else if (currentControl is ImageButton)
            {
                gridView.Controls.Remove(currentControl);
                gridView.Controls.AddAt(i, new LiteralControl((currentControl as ImageButton).AlternateText));
            }
            else if (currentControl is HyperLink)
            {
                gridView.Controls.Remove(currentControl);
                gridView.Controls.AddAt(i, new LiteralControl((currentControl as HyperLink).Text));
            }
            else if (currentControl is DropDownList)
            {
                gridView.Controls.Remove(currentControl);
                gridView.Controls.AddAt(i, new LiteralControl((currentControl as DropDownList).SelectedItem.Text));
            }
            else if (currentControl is CheckBox)
            {
                gridView.Controls.Remove(currentControl);
                gridView.Controls.AddAt(i, new LiteralControl((currentControl as CheckBox).Checked ? "True" : "False"));
            }
            if (currentControl.HasControls())
            {
                // if there is any child controls, call this method to prepare for export
                PrepareGridViewForExport(currentControl);
            }
        }
    }

PrepareGridViewForExport(gridView1);