How do I access a Control inside a XAML DataTemplate?

I have this FlipView:

<FlipView x:Name="models_list" SelectionChanged="selectionChanged">
    <FlipView.ItemTemplate>
        <DataTemplate>
            <Grid x:Name="cv">
                <Image x:Name="img1" Source = "{Binding ModelImage}" Stretch="Fill" Tag="{Binding ModelTag}"/>
            </Grid>
        </DataTemplate>
    </FlipView.ItemTemplate>
</FlipView>

I want to find img1 of currently selected index. While searching for it I found this method on some post here:

    private DependencyObject FindChildControl<T>(DependencyObject control, string ctrlName)
    {
        int childNumber = VisualTreeHelper.GetChildrenCount(control);
        for (int i = 0; i < childNumber; i++)
        {
            DependencyObject child = VisualTreeHelper.GetChild(control, i);
            FrameworkElement fe = child as FrameworkElement;
            // Not a framework element or is null
            if (fe == null) return null;

            if (child is T && fe.Name== ctrlName)
            {
                // Found the control so return
                return child;
            }
            else
            {
                // Not found it - search children
                DependencyObject nextLevel = FindChildControl<T>(child, ctrlName);
                if (nextLevel != null)
                    return nextLevel;
            }
        }
        return null;
    }

It returns me the Image on the first index of FlipView but I need the one present on the currently selected index. I tried to edit this method but I am unable to find the required control. Can anyone help me?