<Style TargetType="{x:Type ToggleButton}">
<Setter Property="Template">
<Setter.Value>
<ControlTemplate TargetType="{x:Type ToggleButton}">
    <Border x:Name="innerBorder">
        <!-- Use one JPEG image as the background of ToggleButton -->
        <Border.Background>
            <ImageBrush ImageSource="C:\Users\Public\Pictures\Sample Pictures\Tree.jpg" />
        </Border.Background>
    </Border>
    <ControlTemplate.Triggers>
        <!-- Change the background image to Dock.jpg when the IsChecked property is True ,
        Otherwise, it will automatically switch to original background image -->
        <Trigger Property="IsChecked" Value="True">
            <Setter TargetName="innerBorder" Property="Background">
                <Setter.Value>
                    <ImageBrush ImageSource="C:\Users\Public\Pictures\Sample Pictures\Dock.jpg" />
                </Setter.Value>
            </Setter>
        </Trigger>
    </ControlTemplate.Triggers>
</ControlTemplate>
</Setter.Value>
</Setter>
</Style>