WPF Image automatically display image via System.Timer.Timer

<Window x:Class="WpfApp10.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:WpfApp10"
        mc:Ignorable="d"
        WindowState="Maximized"
        WindowStyle="None"
        Title="MainWindow" Height="450" Width="800">
    <Window.DataContext>
        <local:MainVM/>
    </Window.DataContext>
    <Grid>
        <Image Source="{Binding ImgUrl,Mode=TwoWay,UpdateSourceTrigger=PropertyChanged}"
               RenderOptions.BitmapScalingMode="HighQuality"/>
        <TextBlock Text="{Binding Num,Mode=TwoWay,UpdateSourceTrigger=PropertyChanged}"
                   HorizontalAlignment="Right"
                   VerticalAlignment="Bottom"
                   Width="150"
                   Foreground="Red"
                   FontSize="50"/>
    </Grid>
</Window>


//cs

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.IO;
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 WpfApp10
{
    /// <summary>
    /// Interaction logic for MainWindow.xaml
    /// </summary>
    public partial class MainWindow : Window
    {
        public MainWindow()
        {
            InitializeComponent();
        }
    }

    public class MainVM : INotifyPropertyChanged
    { 
        public MainVM()
        {
            imgsList =new List<string>(Directory.GetFiles(@"../../Images"));
            if(imgsList!=null && imgsList.Any())
            {
                imgsCount = imgsList.Count();
                imgIdx = 0;
                ImgUrl = imgsList[imgIdx];
            }

            System.Timers.Timer tmr = new System.Timers.Timer();
            tmr.Elapsed += Tmr_Elapsed;
            tmr.Interval = 100;
            tmr.Start();
        }

        private void Tmr_Elapsed(object sender, System.Timers.ElapsedEventArgs e)
        {
            if(++ImgIdx>=imgsCount)
            {
                ImgIdx = 0;
            }
            ++Num;
        }

        public event PropertyChangedEventHandler PropertyChanged;
        private void OnPropertyChanged(string propertyName)
        {
            var handler = PropertyChanged;
            if(handler!=null)
            {
                handler?.Invoke(this, new PropertyChangedEventArgs(propertyName));
            }
        }

        private List<string> imgsList { get; set; }
        private int imgsCount = 0;

        private int imgIdx = 0;
        public int ImgIdx
        {
            get
            {
                return imgIdx;
            }
            set
            {
                if(value!=imgIdx)
                {
                    imgIdx = value;
                    if(imgIdx>=imgsCount)
                    {
                        imgIdx = 0;
                    }
                    OnPropertyChanged(nameof(ImgIdx));
                    ImgUrl = imgsList[ImgIdx];
                }
            }
        }

        private int num = 1;
        public int Num
        {
            get
            {
                return num;
            }
            set
            {
                if(value!=num)
                {
                    num = value;
                    OnPropertyChanged(nameof(Num));
                }
            }
        }

        private string imgUrl;
        public string ImgUrl
        {
            get
            {
                return imgUrl;
            }
            set
            {
                if (value != imgUrl)
                {
                    imgUrl = value;
                    OnPropertyChanged(nameof(ImgUrl));
                }
            }
        }
    }
}