Cannot open many Images in WPF

This is my code:

foreach (Database.Photo photo in eventPhotos)
        {
            Image img = new Image();
            img.Height = 100;
            img.Width = 80;
            img.Focusable = true;
            img.MouseDown += new MouseButtonEventHandler(img_MouseDown);
            string littleString = photo.PhotoUrl;
            littleString = littleString.Replace(".jpg", "t.jpg");
            BitmapImage bi = new BitmapImage();
            bi.Begin开发者_如何学CInit();
            bi.UriSource = new Uri(littleString, UriKind.Absolute);
            bi.EndInit();
            img.Source = bi;
            imagesEvent1.Children.Add(img);
        }

But not all images are loaded.:

in this time, images №3,5 are not loaded, in next time other images are not loaded.

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The image download may be failing. Try handling the ImageFailed event on the Image control and see if that fires.