I have an WPF form that I myself did not create, so I am not very good at WPF. It is leaking badly though, up to 400 MB and closing the form does not help.

The problem lies in my application loading all the pictures at once. I would like to only load the ones visible at the moment. It is about 300 pictures and they are a bit large so my WPF-form suffers from loading them all.

I have a DataTemplate with my own type that has a property Thumbnail. The code in the template is like this:

            <Image Source="{Binding Path=Thumbnail}" Stretch="Fill"/>

And then I have a grid with a control that has the above template as source. The code for this control is the below. Please provide me with hints on how to optimize the code and perhaps get the only ones that are visible and only have that many controls loaded at the same time?

    <Setter Property="Template">
        <Setter.Value>
            <ControlTemplate TargetType="Controls:ElementFlow">
                <Grid Background="{TemplateBinding Background}">
                    <Canvas x:Name="PART_HiddenPanel"
                            IsItemsHost="True"
                            Visibility="Hidden" />
                    <Viewport3D x:Name="PART_Viewport">
                        <!-- Camera -->
                        <Viewport3D.Camera>
                            <PerspectiveCamera FieldOfView="60"
                                               Position="0,1,4"
                                               LookDirection="0,-1,-4"
                                               UpDirection="0,1,0" />
                        </Viewport3D.Camera>

                        <ContainerUIElement3D x:Name="PART_ModelContainer" />

                        <ModelVisual3D>
                            <ModelVisual3D.Content>
                                <AmbientLight Color="White" />
                            </ModelVisual3D.Content>
                        </ModelVisual3D>
                <Viewport2DVisual3D
        RenderOptions.CachingHint="Cache"
        RenderOptions.CacheInvalidationThresholdMaximum="2"
        RenderOptions.CacheInvalidationThresholdMinimum="0.5"/>
                    </Viewport3D>
                </Grid>
            </ControlTemplate>
        </Setter.Value>
    </Setter>
</Style>