public static void Watermark (string imageUrl)
        {
            Stopwatch watch = new Stopwatch ();
            watch.Start ();

            Console.WriteLine ("Starting process");
            string BASE = Directory.GetCurrentDirectory () + "/Images/";

            WebClient client = new WebClient ();
            byte[] data = client.DownloadData (imageUrl);
            Console.WriteLine ("Elapsed: " + watch.ElapsedMilliseconds);

            using (Image image = Image.FromStream (new MemoryStream (data)))
            using (Image watermark = Image.FromFile (BASE + "watermark.png"))
            using (Graphics graphics = Graphics.FromImage (image))
            using (Brush brush = new TextureBrush (watermark)) {

                int x = (image.Width - watermark.Width)/2;
                int y = (image.Height - watermark.Height)/2;

                graphics.FillRectangle(brush, new Rectangle(new Point(x, y), watermark.Size));
                image.Save(BASE + "norma_watermarked.jpg");
            }

            watch.Stop ();
            Console.WriteLine ("Process ended: " + watch.ElapsedMilliseconds);
        }