Wpf-how can I use a converter in order to display elements from a listbox while I am scrolling.

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C#

WCF

WPF

I have a big list which is coming from WCF and i loaded in a Listbox.
I would like to display only the images which are visible on the scroll position. I found on the internet this option but is I can see it don't seems to work very good.
This is the default converter whichc i found on the internet and i modified it in order to work with my program. Unfortunately is not doing anything extra than the default one.

class NullVisibilityConverter : IValueConverter
{
    public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
    {
        return value == null ? Visibility.Hidden : Visibility.Visible;
    }

    public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
    {
        return value == null ? Visibility.Visible : Visibility.Hidden;
    }

I am new in WPF Programming and i got stuck. Does anyone have any idea how to do it?

What I have tried:

I tried to use the scroll position but it don't seems to work. I am using MVVM Pattern for this app.