WPF Image stretch to fill doesn't stretch to the bounds of it's parents

Here's my XAML and how it looks like:

<Window x:Class="GameLenseWpf.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        Title="MainWindow" Height="450" Width="350" MinHeight="450" MinWidth="350">

    <Grid>
        <Grid.RowDefinitions>
            <RowDefinition Height="0.15*" />
            <RowDefinition />
        </Grid.RowDefinitions>
        <Image Grid.Row="0" Stretch="Fill" Source="Image/topBarBg.png" />
        <StackPanel Orientation="Horizontal" Grid.Row="0">
            <TextBlock Text="Platform" 
                       Foreground="White" 
                       FontFamily="Georgia"
                       FontSize="15" 
                       Margin="10"
                       HorizontalAlignment="Center"
                       VerticalAlignment="Center"/>
            <ComboBox x:Name="cmbPlatform" 
                      Margin="10"
                      FontFamily="Georgia"
                      FontSize="15"
                      MinHeight="30"
                      MinWidth="140"
                      VerticalAlignment="Center"
                      VerticalContentAlignment="Center" SelectionChanged="cmbPlatform_SelectionChanged">
                <ComboBoxItem>All Platforms</ComboBoxItem>
                <ComboBoxItem>Playstation 3</ComboBoxItem>
                <ComboBoxItem>XBox 360</ComboBoxItem>
                <ComboBoxItem>Wii</ComboBoxItem>
                <ComboBoxItem>PSP</ComboBoxItem>
                <ComboBoxItem>DS</ComboBoxItem>
            </ComboBox>
        </StackPanel>
        <Image x:Name="imgAbout" Grid.Row="0" Source="Image/about.png" 
               Height="16" HorizontalAlignment="Right"
               VerticalAlignment="Center"
        开发者_如何学C       Margin="0 0 10 0"    />
        <ListBox Grid.Row="1" x:Name="lstGames" Background="#343434" Padding="5"
                 ScrollViewer.HorizontalScrollBarVisibility="Disabled"
                 HorizontalContentAlignment="Stretch">
            <ListBox.Resources>
                <Style TargetType="ListBoxItem">
                    <Style.Resources>
                        <!-- SelectedItem with focus -->
                        <SolidColorBrush x:Key="{x:Static SystemColors.HighlightBrushKey}"
                       Color="Transparent" />
                        <!-- SelectedItem without focus -->
                        <SolidColorBrush x:Key="{x:Static SystemColors.ControlBrushKey}"
                       Color="Transparent" />
                        <!-- SelectedItem text foreground -->
                        <SolidColorBrush x:Key="{x:Static SystemColors.HighlightTextBrushKey}"
                       Color="Black" />
                    </Style.Resources>
                    <Setter Property="FocusVisualStyle" Value="{x:Null}" />
                </Style>
            </ListBox.Resources>
            <ListBox.ItemTemplate>
                <DataTemplate>
                    <Grid Height="120" Margin="0 10" >
                        <Grid.ColumnDefinitions>
                            <ColumnDefinition Width="90"/>
                            <ColumnDefinition />
                        </Grid.ColumnDefinitions>
                        <Grid.RowDefinitions>
                            <RowDefinition />                            
                        </Grid.RowDefinitions>

                        <Border BorderBrush="#202020" BorderThickness="5" CornerRadius="4" Panel.ZIndex="0">
                            <Canvas Grid.Row="0" Grid.Column="0" >
                                <Image Source="{Binding ImageUrl}" Canvas.Left="0" Canvas.Top="0" Stretch="UniformToFill"/>
                                <Image Source="Image/youtube.png" Canvas.Bottom="0" Canvas.Right="0" Height="20" Width="20" />
                            </Canvas>                           
                        </Border>

                        <StackPanel Grid.Row="0" Grid.Column="1" Margin="12 0 0 0">
                            <StackPanel Orientation="Horizontal">
                                <TextBlock Text="Title:" FontFamily="Arial" Foreground="White"/>
                                <TextBlock Text="{Binding Title}" FontFamily="Arial" Foreground="White" />
                            </StackPanel>
                            <StackPanel Orientation="Horizontal">
                                <TextBlock Text="Release Date:" FontFamily="Arial" Foreground="White" />
                                <TextBlock Text="{Binding ReleaseDate}" FontFamily="Arial" Foreground="White" />
                            </StackPanel>
                            <TextBlock Text="Synopsis" FontFamily="Arial" Foreground="White" />
                            <TextBox Background="#454545" Foreground="White" TextWrapping="Wrap" Text="{Binding Synopsis}" MaxHeight="73" />
                        </StackPanel>
                    </Grid>
                </DataTemplate>
            </ListBox.ItemTemplate>
        </ListBox>
    </Grid>
</Window>

I just want to games image to stretch to fill the canvas bounds, which is inside of the rounder border.

Why is it not doing this?

The problem is that you have the images within a canvas. Basically, any time you put an element in a Canvas panel, you are disregarding the entire layout system. Elements within a canvas do not participate in layout at all. What you want to do is replace the Canvas element with a plain Grid element (you don't need to define rows or columns, it will default to a single row/column.)

EDIT

And actually looking more closely at what you are trying to do, you'll need to make some slight tweaks. Try this.

<Border BorderBrush="#202020" BorderThickness="5" CornerRadius="4">
    <Grid>
        <Image Source="{Binding ImageUrl}" Stretch="UniformToFill"/>
        <Image Source="Image/youtube.png" HorizontalAlignment="Right" VerticalAlignment="Bottom" Height="20" Width="20" />
    </Grid>                           
</Border>

your problem is here

<Border BorderBrush="#202020" BorderThickness="5" CornerRadius="4" Panel.ZIndex="0">
    <Canvas Grid.Row="0" Grid.Column="0" >
        <Image Source="{Binding ImageUrl}" Canvas.Left="0" Canvas.Top="0" Width="80" Stretch="Fill"/>
        <Image Source="Image/youtube.png" Canvas.Bottom="0" Canvas.Right="0" Height="20" Width="20" />
    </Canvas>                           
</Border>

you have a BorderThickness Attribute which puts the black border around the image, just remove it or set it to 0 and this will solve the problem.

so your code will be

<Border BorderBrush="#202020" CornerRadius="4" Panel.ZIndex="0">
    <Canvas Grid.Row="0" Grid.Column="0" >
        <Image Source="{Binding ImageUrl}" Canvas.Left="0" Canvas.Top="0" Width="80" Stretch="Fill"/>
        <Image Source="Image/youtube.png" Canvas.Bottom="0" Canvas.Right="0" Height="20" Width="20" />
    </Canvas>                           
</Border>

or

<Border BorderBrush="#202020" BorderThickness="0" CornerRadius="4" Panel.ZIndex="0">
    <Canvas Grid.Row="0" Grid.Column="0" >
        <Image Source="{Binding ImageUrl}" Canvas.Left="0" Canvas.Top="0" Width="80" Stretch="Fill"/>
        <Image Source="Image/youtube.png" Canvas.Bottom="0" Canvas.Right="0" Height="20" Width="20" />
    </Canvas>                           
</Border>