error in memory match up game in windows phone 8 using c#.

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C#

XAML

In the following Code i'm unable to compare the pending image values.

public partial class MainPage : PhoneApplicationPage
{
Image PendingImage1;
Image PendingImage2;

public void img1_Tap(object sender, System.Windows.Input.GestureEventArgs e)
{
this.img1.Source = new BitmapImage(new Uri("Assets/baby.jpg", UriKind.RelativeOrAbsolute));
if (PendingImage1 == null)
{
PendingImage1 = img1;
}
else if (PendingImage1 != null && PendingImage2 == null)
{
PendingImage2 = img1;
}
if (PendingImage1 != null && PendingImage2 != null)
{
if (PendingImage1.Tag == PendingImage2.Tag)
{

}
else
{
DispatcherTimer timer = new DispatcherTimer();
timer.Start();
}

}
}

private void img2_Tap(object sender, System.Windows.Input.GestureEventArgs e)
{

this.img2.Source = new BitmapImage(new Uri("Assets/duckk.jpg", UriKind.RelativeOrAbsolute));
if (PendingImage1 == null)
{
PendingImage1 = img2;
}
else if (PendingImage1 != null && PendingImage2 == null)
{
PendingImage2 = img2;
}
if (PendingImage1 != null && PendingImage2 != null)
{
if (PendingImage1.Tag == PendingImage2.Tag)
{

}
else
{
DispatcherTimer timer = new DispatcherTimer();
timer.Start();
}

}
}