Take a look at following example:
<TabControl>
<TabControl.Resources>
<DataTemplate x:Key="tabItemGeneralHeaderTemplate">
<StackPanel Orientation="Horizontal" Margin="0,-3,0,0">
<Image Name="tabGeneralImg" Source="Image/tabGeneralActive.png" Width="11" Height="11"></Image>
<Label Name="tabGeneralLbl" Content="General"></Label>
</StackPanel>
<DataTemplate.Triggers>
<DataTrigger Binding="{Binding Path=IsSelected,RelativeSource={RelativeSource TemplatedParent}}" Value="True">
<Setter TargetName="tabGeneralImg" Property="Source" Value="Images/tabGeneral.png"/>
</DataTrigger>
</DataTemplate.Triggers>
</DataTemplate>
</TabControl.Resources>
<TabItem Name="tabItemGeneral" HeaderTemplate="{StaticResource tabItemGeneralHeaderTemplate}">
<Grid>
...
</Grid>
</TabItem>
</TabControl>
Just change the source property of the images to some path in your file system and you should do fine :)