请问如何获取按钮的背景图片。以供后面的页面使用。如何定义如何获取呢？

<Window x:Class="WpfCoupon.Window1"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    Title="Window1" Height="573" Width="612">
    <Grid Height="514" Width="572">
        <Button HorizontalAlignment="Left" Margin="20,22,0,0" Name="button1" Width="136" Height="142" VerticalAlignment="Top" Click="button1_Click">
                <Image Source=".\Images\wpf.jpg" Stretch="Fill" ImageFailed="Image_ImageFailed" Height="142" Width="136" />
        </Button>
        <Button Height="142" Width="136" Margin="184,22,240,0" Name="button2" VerticalAlignment="Top" Click="button2_Click">
            <Image Source=".\Images\a.jpg" Stretch="Fill"/>
        </Button>
    </Grid>
</Window>