splitter/Splitter-UI/Views/PreviewPane.axaml

<UserControl
    xmlns="https://github.com/avaloniaui"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    x:Class="Splitter_UI.Views.PreviewPane"
    xmlns:vm="clr-namespace:Splitter_UI.ViewModels"
    x:DataType="vm:PreviewPaneViewModel">

    <Border Background="#202020" Padding="10">
        <Grid>
            <Image Source="{Binding Selected.Preview.Frame}" Stretch="Uniform"/>

            <!-- Optional overlays -->
            <ItemsControl ItemsSource="{Binding Selected.Preview.FaceBoxes}">
                <ItemsControl.ItemTemplate>
                    <DataTemplate>
                        <Border BorderBrush="Lime" BorderThickness="2"
                                Width="{Binding Width}" Height="{Binding Height}"
                                Canvas.Left="{Binding X}" Canvas.Top="{Binding Y}"/>
                    </DataTemplate>
                </ItemsControl.ItemTemplate>
            </ItemsControl>
        </Grid>
    </Border>
</UserControl>