Eu uso um controle personalizado chamadoImageButton para exibir um botão com imagens diferentes.ImageButton contém propriedades de dependência:

public ImageSource DisabledImageSource
    {
        get { return (ImageSource)GetValue(DisabledImageSourceProperty); }
        set { SetValue(DisabledImageSourceProperty, value); }
    }


    public ImageSource NormalImageSource
    {
        get { return (ImageSource)GetValue(NormalImageSourceProperty); }
        set { SetValue(NormalImageSourceProperty, value); }
    }

    public ImageSource HoverImageSource
    {
        get { return (ImageSource)GetValue(HoverImageSourceProperty); }
        set { SetValue(HoverImageSourceProperty, value); }
    }

    public ImageSource PushedImageSource
    {
        get { return (ImageSource)GetValue(PushedImageSourceProperty); }
        set { SetValue(PushedImageSourceProperty, value); }
    }


    public static readonly DependencyProperty DisabledImageSourceProperty =
        DependencyProperty.Register("DisabledImageSource", typeof(ImageSource), typeof(ImageButton), new UIPropertyMetadata());


    public static readonly DependencyProperty NormalImageSourceProperty =
        DependencyProperty.Register("NormalImageSource", typeof(ImageSource), typeof(ImageButton), new UIPropertyMetadata());


    public static readonly DependencyProperty HoverImageSourceProperty =
        DependencyProperty.Register("HoverImageSource", typeof(ImageSource), typeof(ImageButton), new UIPropertyMetadata());

    public static readonly DependencyProperty PushedImageSourceProperty =
        DependencyProperty.Register("PushedImageSource", typeof(ImageSource), typeof(ImageButton), new UIPropertyMetadata());

Seu estilo é definido da seguinte maneira:

<Style TargetType="{x:Type local:ImageButton}">
    <Setter Property="HorizontalAlignment" Value="Left"/>
    <Setter Property="Template">
        <Setter.Value>
            <ControlTemplate TargetType="{x:Type Button}">
                <Grid>
                    <Image Name="image" Source="{Binding NormalImageSource, RelativeSource={RelativeSource TemplatedParent}}" Stretch="None" />
                </Grid>
                <ControlTemplate.Triggers>                    
                    <Trigger Property="IsEnabled" Value="False">
                        <Setter TargetName="image" Property="Source" Value="{Binding DisabledImageSource, RelativeSource={RelativeSource TemplatedParent}}"/>
                    </Trigger>
                    <Trigger Property="Button.IsPressed" Value="True">
                        <Setter TargetName="image" Property="Source"  Value="{Binding PushedImageSource, RelativeSource={RelativeSource TemplatedParent}}"/>
                    </Trigger>
                    <MultiTrigger>
                        <MultiTrigger.Conditions>
                            <Condition Property="IsMouseOver" Value="True" />
                        </MultiTrigger.Conditions>
                        <Setter TargetName="image" Property="Source" Value="{Binding HoverImageSource, RelativeSource={RelativeSource TemplatedParent}}"/>
                    </MultiTrigger>
                </ControlTemplate.Triggers>
            </ControlTemplate>
        </Setter.Value>
    </Setter>
</Style>

Tudo funciona bem, excetoIsPressed. Eu nunca consigo ver a imagem que eu coloqueiPushedImageSource e eu não consigo descobrir o porquê. Qualquer ajuda seria apreciada :)

EDIT 1:

Aqui está o código xaml que testa isso

<Window x:Class="SMEClient.WPF.Tester.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:is="clr-namespace:Project1.SearchBox;assembly=Project1"
        Title="MainWindow" Height="350" Width="525">
    <Window.Resources>
        <ResourceDictionary>
            <ResourceDictionary.MergedDictionaries>
                <ResourceDictionary Source="pack://application:,,,/Project1;component/SearchBox/ImageButton.xaml"/>
            </ResourceDictionary.MergedDictionaries>
        </ResourceDictionary>
    </Window.Resources>
    <Grid>
        <StackPanel>
            <is:ImageButton NormalImageSource="C:\Users\Public\Pictures\Sample Pictures\Koala.jpg"
                            PushedImageSource="C:\Users\Public\Pictures\Sample Pictures\Chrysanthemum.jpg"
                            HoverImageSource="C:\Users\Public\Pictures\Sample Pictures\Jellyfish.jpg"/>
        </StackPanel>
    </Grid>
</Window>