How to add water mark on image upload

below my code for uploading image

protected void OnUpdate(object sender, EventArgs e)
{
    System.IO.Stream fs = FileUpload2.PostedFile.InputStream;
    System.IO.BinaryReader br = new System.IO.BinaryReader(fs);
    Byte[] bytesM = br.ReadBytes((Int32)fs.Length);

i gone through your reference which is about image in folder, but i am inserting image into database