<Window x:Class="TestApp.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        Title="MainWindow" Height="350" Width="525" WindowStyle="None" ResizeMode="NoResize" WindowState="Maximized" Loaded="Window_Loaded">
    <Window.Resources>
    </Window.Resources>
    <Grid>
        <Image Source="pack://application:,,,/Images/backgraund.jpg" Stretch="Fill" Margin="0"/>
        <Image Stretch="None" x:Name="imgOblaka">
        </Image>
        <Button Content="Button" HorizontalAlignment="Left" Margin="144,153,0,0" VerticalAlignment="Top" Width="75" Click="Button_Click"/>
    </Grid>
</Window>

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.Media.Animation;
using System.Windows.Navigation;
using System.Windows.Shapes;
 
namespace TestApp
{
    /// <summary>
    /// Логика взаимодействия для MainWindow.xaml
    /// </summary>
    public partial class MainWindow : Window
    {
        Storyboard oblakaStoryBoard;
        BitmapImage[] bmps;
        const int numofbmps = 1493;
        public MainWindow()
        {
            InitializeComponent();
            bmps = new BitmapImage[numofbmps];
            for (int i = 0; i < numofbmps; i++)
            {
                bmps[i] = new BitmapImage(new Uri(@"Images/Oblaka/oblaka_" + String.Format("{0:00000}", i) + ".png", UriKind.RelativeOrAbsolute));
            }
        }
 
        private void Window_Loaded(object sender, RoutedEventArgs e)
        {
            oblakaStoryBoard = new Storyboard();
            ObjectAnimationUsingKeyFrames oaukf = new ObjectAnimationUsingKeyFrames();
            oaukf.BeginTime = TimeSpan.FromSeconds(0);
            oaukf.RepeatBehavior = RepeatBehavior.Forever;
            Storyboard.SetTarget(oaukf, imgOblaka);
            Storyboard.SetTargetProperty(oaukf, new PropertyPath(Image.SourceProperty));
            for (int i = 0; i < numofbmps; i++)
            {
                DiscreteObjectKeyFrame dokf = new DiscreteObjectKeyFrame(bmps[i], TimeSpan.FromMilliseconds(i*40));
                oaukf.KeyFrames.Add(dokf);
            }
            oblakaStoryBoard.Children.Add(oaukf);
        }
 
        private void Button_Click(object sender, RoutedEventArgs e)
        {
            oblakaStoryBoard.Begin();
        }
    }
}