Arge/Arge/Styles/BlurredDecorationWindow.xaml

<resources:CachedResourceDictionary xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
                                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
                                    xmlns:resources="clr-namespace:Arge.Resources"
                                    xmlns:buttons="clr-namespace:Arge.Controls.Buttons"
                                    xmlns:window="clr-namespace:Arge.Controls.Window">

    <resources:CachedResourceDictionary.MergedDictionaries>
        <resources:CachedResourceDictionary Source="/Arge;component/Styles/ImageButton.xaml" />
        <resources:CachedResourceDictionary Source="/Arge;component/Converter/Converter.xaml" />
    </resources:CachedResourceDictionary.MergedDictionaries>

    <Style x:Key="StyleImageButtonWindow"
           BasedOn="{StaticResource StyleImageButtonWithOpacity}"
           TargetType="{x:Type buttons:ImageButton}">
        <Setter Property="Padding" Value="4" />
        <Setter Property="Margin" Value="4" />
        <Setter Property="VerticalAlignment" Value="Top" />
        <Setter Property="Width" Value="24" />
        <Setter Property="Height" Value="24" />
    </Style>

    <Style x:Key="StyleBlurredDecorationWindow" 
           TargetType="{x:Type window:BlurredDecorationWindow}">
        <Setter Property="WindowStyle" Value="None" />
        <Setter Property="ResizeMode" Value="CanResize" />
        <Setter Property="AllowsTransparency" Value="True" />
        <Setter Property="HorizontalContentAlignment" Value="Stretch" />
        <Setter Property="VerticalContentAlignment" Value="Stretch" />
        <Setter Property="BorderThickness" Value="1,0,1,1" />
        <Setter Property="DecorationHeight" Value="80" />
        <Setter Property="BorderBrush" Value="{DynamicResource BrushWindowBorder}" />
        <Setter Property="Background" Value="{DynamicResource BrushWindowBackground}" />
        <Setter Property="BackgroundImage" Value="{Binding Source={x:Static resources:ImageSources.Instance}, Path=WindowBackground}" />
        <Setter Property="MinWidth" Value="256" />
        <Setter Property="MinHeight" Value="144" />
        <Setter Property="SnapsToDevicePixels" Value="True" />

        <Setter Property="WindowChrome.WindowChrome">
            <Setter.Value>
                <WindowChrome CaptionHeight="0" ResizeBorderThickness="5" />
            </Setter.Value>
        </Setter>

        <Setter Property="Template">
            <Setter.Value>
                <ControlTemplate TargetType="{x:Type window:BlurredDecorationWindow}">
                    <Grid Background="{TemplateBinding Background}">
                        <Grid Margin="-12,-12,-12,0">
                            <Viewbox HorizontalAlignment="Center" Stretch="UniformToFill">
                                <Image Source="{TemplateBinding BackgroundImage}" />
                            </Viewbox>

                            <Border Name="BlurImage">
                                <Border.OpacityMask>
                                    <VisualBrush TileMode="None" Stretch="None" AlignmentX="Center" AlignmentY="Center">
                                        <VisualBrush.Visual>
                                            <Grid Width="{Binding ActualWidth, RelativeSource={RelativeSource AncestorType=Border}}" 
                                                  Height="{Binding ActualHeight, RelativeSource={RelativeSource AncestorType=Border}}">
                                                <Grid.RowDefinitions>
                                                    <RowDefinition Height="12" />
                                                    <RowDefinition Height="92" />
                                                    <RowDefinition Height="*" />
                                                </Grid.RowDefinitions>
                                                <Rectangle Fill="Black" Grid.Row="0" Grid.RowSpan="2" />
                                                <Rectangle Fill="Transparent" Grid.Row="2" />
                                            </Grid>
                                        </VisualBrush.Visual>
                                    </VisualBrush>
                                </Border.OpacityMask>

                                <Border.Effect>
                                    <BlurEffect Radius="30" />
                                </Border.Effect>

                                <Viewbox HorizontalAlignment="Center" Stretch="UniformToFill">
                                    <Image Source="{TemplateBinding BackgroundImage}" VerticalAlignment="Center" HorizontalAlignment="Center" />
                                </Viewbox>
                            </Border>
                        </Grid>

                        <Border BorderBrush="{TemplateBinding BorderBrush}"
                                BorderThickness="{TemplateBinding BorderThickness}">
                            <DockPanel LastChildFill="True">
                                <Border x:Name="PART_Decoration" 
                                        DockPanel.Dock="Top"
                                        HorizontalAlignment="Stretch"
                                        Height="{TemplateBinding DecorationHeight}"
                                        Background="{TemplateBinding BorderBrush}">
                                    <DockPanel HorizontalAlignment="Stretch" Margin="4" LastChildFill="False">
                                        <buttons:ImageButton x:Name="PART_CloseButton"
                                                              DockPanel.Dock="Right"
                                                              Style="{StaticResource StyleImageButtonWindow}"
                                                              Image="{Binding Source={x:Static resources:ImageSources.Instance}, Path=WindowClose}" 
                                                              ToolTip="Close" />

                                        <buttons:ImageButton x:Name="PART_MinimizeButton"
                                                              DockPanel.Dock="Right"
                                                              Style="{StaticResource StyleImageButtonWindow}"
                                                              Image="{Binding Source={x:Static resources:ImageSources.Instance}, Path=WindowMinimize}" 
                                                              ToolTip="Minimize" />

                                        <buttons:ImageButton x:Name="PART_IconButton"
                                                              DockPanel.Dock="Left" 
                                                              VerticalAlignment="Center"
                                                              Margin="8"
                                                              Style="{StaticResource StyleImageButtonWithOpacity}"
                                                              Image="{TemplateBinding Icon}"
                                                              ToolTip="http://arge.be" />
                                    </DockPanel>
                                </Border>

                                <ContentPresenter x:Name="PART_Content" />
                            </DockPanel>
                        </Border>
                    </Grid>
                </ControlTemplate>
            </Setter.Value>
        </Setter>
    </Style>

</resources:CachedResourceDictionary>