Gif animation with the directional keys

Question

I am creating a 2D platform game in a wpf application... and I tried to make my character walk with a gif animation.

Here's my C# code:

private void imgMega_OnKeyDown(object sender, KeyEventArgs e)
        {
            if (e.Key == Key.Right)
            {
                if (Grid.GetColumn(imgMega) <= Grid.ColumnDefinitions.Count - 1)
                    Grid.SetColumn(imgMega, Grid.GetColumn(imgMega) + 1);
                BitmapImage bmi = new BitmapImage(new Uri("megaman.gif", UriKind.Relative));
                imgMega.Source = bmi;

            }
        } /*---- When my character walk ----*/

        private void imgMega_OnKeyUp(object sender, KeyEventArgs e)
        {
            BitmapImage bmi = new BitmapImage(new Uri("Megaman8bit.jpg", UriKind.Relative));
            imgMega.Source = bmi;
        } /*---- When my character stop walking ----*/

And my XAML code:

<Image Name="imgMega" Width="60" Grid.ColumnSpan="4" FocusVisualStyle="{x:Null}" Source="Megaman8bit.jpg" Focusable="True" KeyDown="imgMega_OnKeyDown" KeyUp="imgMega_OnKeyUp"/>

* My "megaman.gif" image is my walking character and my "Megaman8bit.jpg" image is my immobile character. *

With this code, the character changes his position but the gif animation doesn't work... Somebody can help me to find what's wrong ?