private void button1_Click(object sender, RoutedEventArgs e)
    {
      BitmapImage bm1 = new BitmapImage();
      bm1.BeginInit();
      Uri uri = new Uri("http://КакойТоАдрес/cam_1.jpg");
      bm1.UriSource = uri;
      bm1.CacheOption = BitmapCacheOption.None;
      bm1.EndInit();
      MyImage.Source = bm1;
    }