silverlight - ListBox items orientation horizontal when using image in ItemTemplate

ListBox items orientation horizontal when using image in ItemTemplate in silverlight
MainPage.xaml

<UserControl 
    x:Class="SilverlightApps.MainPage"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
    mc:Ignorable="d"
    d:DesignHeight="600" 
    d:DesignWidth="800" 
    xmlns:sdk="http://schemas.microsoft.com/winfx/2006/xaml/presentation/sdk"
    >

    <Grid x:Name="LayoutRoot" Background="White">
        <Rectangle
            Name="Rectangle1"
            Fill="AliceBlue" 
            HorizontalAlignment="Left" 
            Height="82" 
            Margin="20,12,0,0" 
            Stroke="Black" 
            VerticalAlignment="Top" 
            Width="750"
            StrokeThickness="0"
            />

        <TextBlock 
            Name="TextBlock1" 
            Height="82" 
            HorizontalAlignment="Left" 
            Margin="20,9,0,0" 
            Text="ListBox items orientation horizontal when using image in ItemTemplate in silverlight"
            VerticalAlignment="Top"
            TextWrapping="Wrap"
            FontSize="20"
            FontStyle="Italic"
            Foreground="MidnightBlue"
            Width="600"
            Padding="25,10,10,0"
            />

        <ListBox 
            Name="ListBox1" 
            BorderThickness="1" 
            BorderBrush="LightSkyBlue" 
            Margin="20,116,0,382"
            HorizontalAlignment="Left"
            FontSize="13"
            Width="750"
            Padding="5,10,5,10"
            >
            <ListBox.ItemsPanel>
                <ItemsPanelTemplate>
                    <StackPanel Orientation="Horizontal" />
                </ItemsPanelTemplate>
            </ListBox.ItemsPanel>
            <ListBox.ItemTemplate>
                <DataTemplate>
                    <StackPanel Orientation="Horizontal" VerticalAlignment="Top" Width="280">
                        <Image
                            Source="{Binding ImageURL}"
                            Width="75"
                            />
                        <StackPanel Orientation="Vertical">
                            <TextBlock
                                Text="{Binding BookName}" 
                                Foreground="MidnightBlue"
                                FontFamily="Georgia"
                                FontWeight="Bold"
                                FontSize="14"
                                TextWrapping="Wrap"
                                Width="200"
                                Padding="5,0,0,0"
                                />
                            <TextBlock 
                                Text="{Binding Author}" 
                                Foreground="DimGray"
                                FontFamily="Comic Sans MS"
                                FontStyle="Italic"
                                TextWrapping="Wrap"
                                Width="200"
                                Padding="5,0,0,0"
                                />
                            <TextBlock 
                                Text="{Binding Price}" 
                                Foreground="Magenta"
                                FontFamily="Courier New"
                                FontWeight="ExtraBlack"
                                TextWrapping="Wrap"
                                Width="200"
                                Padding="5,0,0,0"
                                />
                        </StackPanel>
                    </StackPanel>
                </DataTemplate>
            </ListBox.ItemTemplate>
        </ListBox>
    </Grid>
</UserControl>
MainPage.xaml.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Net;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Animation;
using System.Windows.Shapes;

namespace SilverlightApps
{
    public partial class MainPage : UserControl
    {
        public MainPage()
        {
            InitializeComponent();

            List<Book> Books = new List<Book>();

            // this blog are not the books images owner
            //we uses those images here only for examples
            //image collect from as ImageURL (image source)

            Books.Add(
                new Book(
                        "ASP.NET 4 24-Hour Trainer",
                        "Toi B. Wright",
                        "US $44.99",
                        "http://media.wiley.com/product_data/coverImage/10/04705969/0470596910.jpg"
                        )
                    );

            Books.Add(
                new Book(
                        "Beginning Flash, Flex, and AIR Development for Mobile Devices",
                        "Jermaine G. Anderson",
                        "US $39.99",
                        "http://media.wiley.com/product_data/coverImage/59/04709481/0470948159.jpg"
                        )
                    );

            Books.Add(
                new Book(
                        "SharePoint Server 2010 Administration 24 Hour Trainer",
                        "Bill Crider, Martin Reid, Clint Richardson",
                        "US $34.99",
                        "http://media.wiley.com/product_data/coverImage/60/04709390/0470939060.jpg"
                        )
                    );

            Books.Add(
                new Book(
                        "Professional Mobile Web Development with WordPress, Joomla! and Drupal",
                        "James Pearce",
                        "US $29.99",
                        "http://media.wiley.com/product_data/coverImage/58/11180876/1118087658.jpg"
                        )
                    );

            Books.Add(
                new Book(
                        "Beginning iOS Game Development",
                        "Patrick Alessi",
                        "US $39.99",
                        "http://media.wiley.com/product_data/coverImage/22/11181073/1118107322.jpg"
                        )
                    );

            ListBox1.ItemsSource = Books;
        }

        public class Book
        {
            public String BookName { get; set; }
            public String Author { get; set; }
            public String Price { get; set; }
            public String ImageURL { get; set; }

            public Book(String bookname, String author, String price, String imageurl)
            {
                this.BookName = bookname;
                this.Author = author;
                this.Price = price;
                this.ImageURL = imageurl;
            }
        }
    }
}
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