WPF dependency property to customize control in usercontrol

//usercontrol
<UserControl x:Class="WpfApp157.ImageListBox"
             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
             xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" 
             xmlns:d="http://schemas.microsoft.com/expression/blend/2008" 
             xmlns:local="clr-namespace:WpfApp157"
             mc:Ignorable="d" 
             d:DesignHeight="450" d:DesignWidth="800">
    <Grid>
        <Grid.ColumnDefinitions>
            <ColumnDefinition Width="200"/>
            <ColumnDefinition />
        </Grid.ColumnDefinitions>
        <ListBox Grid.Column="0" x:Name="lbx">
            <ListBox.ItemTemplate>
                <DataTemplate>
                    <Image Width="200" Height="500" Source="{Binding Content,RelativeSource={RelativeSource AncestorType=ListBoxItem}}"/>
                </DataTemplate>
            </ListBox.ItemTemplate>
        </ListBox>
        <Image Grid.Column="1" x:Name="img" Source="{Binding SelectedItem,ElementName=lbx}">            
        </Image>
    </Grid>
</UserControl>


//usercontrol.cs
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Data;
using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Imaging;
using System.Windows.Navigation;
using System.Windows.Shapes;

namespace WpfApp157
{
    /// <summary>
    /// Interaction logic for ImageListBox.xaml
    /// </summary>
    public partial class ImageListBox : UserControl
    {
        public List<string> LbxItemSource
        {
            get { return (List<string>)GetValue(LbxItemSourceProperty); }
            set { SetValue(LbxItemSourceProperty, value); }
        }

        // Using a DependencyProperty as the backing store for LbxItemSource.  This enables animation, styling, binding, etc...
        public static readonly DependencyProperty LbxItemSourceProperty =
            DependencyProperty.Register("LbxItemSource", typeof(List<string>), 
                typeof(ImageListBox), new PropertyMetadata(null,LbxItemsSourceChangedCallBack));

        private static void LbxItemsSourceChangedCallBack(DependencyObject d, DependencyPropertyChangedEventArgs e)
        {
            var lbxControl = d as ImageListBox;
            if(lbxControl == null)
            {
                return;
            }
            lbxControl.lbx.ItemsSource = e.NewValue as List<string>;
            lbxControl.lbx.SelectedIndex = 0;
        }

        public ImageListBox()
        {
            InitializeComponent();
        }
    }
}

//main.xaml
<Window x:Class="WpfApp157.MainWindow"
        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"
        xmlns:local="clr-namespace:WpfApp157"
        mc:Ignorable="d"
        Title="MainWindow" Height="450" Width="800">
    <Grid>
        <local:ImageListBox LbxItemSource="{Binding  ImgsList,Mode=TwoWay,UpdateSourceTrigger=PropertyChanged}"/>
    </Grid>
</Window>


//main.xaml.cs
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Data;
using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Imaging;
using System.Windows.Navigation;
using System.Windows.Shapes;
using System.IO;

namespace WpfApp157
{
    /// <summary>
    /// Interaction logic for MainWindow.xaml
    /// </summary>
    public partial class MainWindow : Window
    {

         public List<string> ImgsList {  get; set; }
        public MainWindow()
        {
            InitializeComponent();
            var files = Directory.GetFiles(@"..\..\Images")?.ToList();
            ImgsList = new List<string>(files);
            this.DataContext = this;
        }
    }
}