Binding an image in a datatemplate - wpf

Question

I'm trying to add a menu to my application, I'd like that my menu header is the currently connected user's picture.
My issue is that every binding works except the one for the image, from what I've understood on the net the DataTemplate I use to replace the menu header by a picture doesn't have access to it's parent Datacontext. I tried to use some stuff like relative source and other tricks but with no luck (certainely related to the fact that I'm new in mvvm and I obviously still have a lot to learn :) )
Here's the code I'm using :
<Grid DataContext="{Binding User}">
<DockPanel>
<Label Content="{Binding Strings.Hello, Source={StaticResource StringLocalizer} }" VerticalAlignment="Center" Padding="0,0,5,0" FontFamily="{DynamicResource Font_Normal}" FontSize="15" Foreground="White"/>
<TextBlock Text="{Binding DisplayName, TargetNullValue='Guest', FallbackValue='Guest'}" VerticalAlignment="Center" HorizontalAlignment="Left" FontFamily="{DynamicResource Font_Normal}" FontSize="15" Foreground="White"/>
<Menu Name="LogonMenu" Margin="10,0,0,0" DataContext="{Binding User}">
<MenuItem >
<MenuItem.HeaderTemplate>
<DataTemplate>
<!--<Image Source="{Binding Datacontext.Image,RelativeSource={RelativeSource FindAncestor, AncestorType={x:Type Application}}, Converter={StaticResource ImageConverter}, FallbackValue={StaticResource DefaultUserIcon}}"/>-->
<Image DataContext="{Binding User}" Source="{Binding Path=Image, Converter={StaticResource ImageConverter}, FallbackValue={StaticResource DefaultUserIcon},Mode=TwoWay}"/>
</DataTemplate>
</MenuItem.HeaderTemplate>
<MenuItem Header="{Binding Strings.SignIn, Source={StaticResource StringLocalizer}}" Width="150" Margin="10,0,0,0" IsEnabled="{Binding Connected, Converter={StaticResource BoolInverterConverter}}" Visibility="{Binding RelativeSource={RelativeSource Mode=Self},Path=IsEnabled, Converter={StaticResource BoolToVisibilityConverter}}" Command="{Binding RelativeSource={RelativeSource AncestorType=Window},Path=DataContext.SignInCommand}"/>
<MenuItem Header="{Binding Strings.SignOut, Source={StaticResource StringLocalizer}}" Margin="10,0,0,0" IsEnabled="{Binding Connected}" Visibility="{Binding RelativeSource={RelativeSource Mode=Self},Path=IsEnabled, Converter={StaticResource BoolToVisibilityConverter}}" Command="{Binding RelativeSource={RelativeSource AncestorType=Window},Path=DataContext.SignOutCommand}"/>
<MenuItem Header="{Binding Strings.UserInformation, Source={StaticResource StringLocalizer}}" Margin="10,0,0,0" IsEnabled="{Binding Connected}" Visibility="{Binding RelativeSource={RelativeSource Mode=Self},Path=IsEnabled, Converter={StaticResource BoolToVisibilityConverter}}"/>
</MenuItem>
</Menu>
</DockPanel>
</Grid>
In my case the image always shows the fallback picture, if someone could help me finding a way to have my user's picture it would be great.