how to watermark multiple images at a time

hi everyone,
in my project i am allowing user to select multiple images at a time and i am passing the ids of these images to next page WATERMARK...
in the WATERMARK page i am allowing users to select combos like for a particular image id they are able to select different messages to embed...
but it performs watermark on only one image id which is selected at the end....
here is a piece of my code...plz help..how to make sure that all the image id selected gets watermarked...
 public void Button1_Click(object sender, EventArgs e)
    {


        ConnectionStringSettings set = ConfigurationManager.ConnectionStrings["WATERMARKING"];
        String cns = set.ConnectionString;
        SqlConnection connection = new SqlConnection(cns);
        connection.Op ...