Tabitem header image - wpf

Question

When I set image as Header of TabItem it looks like image in some gray area. How remove this surrouding area?
<TabControl TabStripPlacement="Left"
HorizontalContentAlignment="Left"
VerticalContentAlignment="Top">
<TabItem ToolTip="Элементы, в которых найдены несоответствия" Height="200"
Style="{StaticResource TabItemHeaderImageStyle}">
<TabItem.Header>
<Image Source="{StaticResource CheckImage}"
Margin="0"
Height="25" Width="25" />
</TabItem.Header>
<ListBox ItemsSource="{Binding unmatched.vs}"
MaxHeight="200"
ItemTemplate="{StaticResource VertexPresenterNotConformTemplate}" />
</TabItem>
<TabItem ToolTip="Элементы, соответствующие шаблону"
Style="{StaticResource TabItemHeaderImageStyle}">
<TabItem.Header>
<Image Source="{StaticResource UncheckImage}"
Height="25" Width="25" />
</TabItem.Header>
<ListBox ItemsSource="{Binding unmatched.vs}"
MaxHeight="200"
ItemTemplate="{StaticResource VertexPresenterConformTemplate}" />
</TabItem>
<Style x:Key="TabItemHeaderImageStyle" TargetType="{x:Type TabItem}">
<Setter Property="Template">
<Setter.Value>
<ControlTemplate TargetType="{x:Type TabItem}">
<Grid>
<Border Name="Border"
Margin="0,0,-4,0"
BorderThickness="1,1,1,1"
CornerRadius="2,12,0,0" >
<ContentPresenter x:Name="ContentSite"
VerticalAlignment="Center"
HorizontalAlignment="Center"
ContentSource="Header"
Margin="12,2,12,2"
RecognizesAccessKey="True"/>
</Border>
</Grid>
</ControlTemplate>
</Setter.Value>
</Setter>
</Style>
What I wish(TabItem's headers under each other without a gray area around it):

Answer 1

TabItem probably has a border around it's header that's gray (thus making a shadow around an image). See this link for TabItem ControlTemplate.
I'd try fiddling with the controltemplate or use an app like WpfInspector to see what's wrong with the template and get correct values.