<Style TargetType="ToggleButton" x:Key="OnOffToggleButtonStyle">
            <Style.Triggers>
                <Trigger Property="IsChecked" Value="True">
                    <Setter Property="Content" Value="СЮДА ЗАПИСАТЬ Image из ресурса самой кнопки" />
                </Trigger>
                <Trigger Property="IsChecked" Value="False">
                    <Setter Property="Content" Value="СЮДА ЗАПИСАТЬ Image из ресурса самой кнопки" />
                </Trigger>
            </Style.Triggers>
        </Style>

                <ToggleButton Padding="3" Style="{StaticResource OnOffToggleButtonStyle}">
                    <ToggleButton.Resources>
                        <Image x:Key="OnImage" Source="Images\OnImg.bmp" />
                        <Image x:Key="OffImage" Source="Images\OffImg.bmp" />
                    </ToggleButton.Resources>
                </ToggleButton>

                <Trigger Property="IsChecked" Value="True">
                    <Setter Property="Content" Value="{DynamicResource ResourceKey=OnImage}" />
                </Trigger>