How to: Style a Separator Used as a Menu Item
Separator controls inside Menu elements appear differently from Separator controls outside a Menu. When you create a Menu with a Separator the control automatically applies the Style identified by SeparatorStyleKey. Styles are placed in resource dictionaries and are searched for by their keys. To change the Style of a Separator inside a Menu, you must use the SeparatorStyleKey property to create your new Style. The following example demonstrates this.
Example
<Style x:Key="{x:Static MenuItem.SeparatorStyleKey}" TargetType="{x:Type Separator}">
<Setter Property="OverridesDefaultStyle" Value="true" />
<Setter Property="Template">
<Setter.Value>
<ControlTemplate TargetType="{x:Type Separator}">
<Image Width="50" Height="30" Source="data\separator.png"/>
</ControlTemplate>
</Setter.Value>
</Setter>
</Style>
For the complete sample see Menu Styles Sample.