This example show how to use Microsoft Cognitive Services Face Detect API in Xamarin.Forms applications - http://julianocustodio.com/facedetect-xamarin-forms

MainPage.xaml

<?xml version="1.0" encoding="utf-8" ?>
<ContentPage xmlns="http://xamarin.com/schemas/2014/forms"
             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
             x:Class="DemoFaceDetect.MainPage">
    <ScrollView>
        <StackLayout>
            <StackLayout Orientation="Horizontal" 
                         HorizontalOptions="Center" 
                         VerticalOptions="Center">
                <Image x:Name="MinhaImagem" Aspect="AspectFill" HeightRequest="200" 
                       WidthRequest="400" HorizontalOptions="CenterAndExpand" />
            </StackLayout>
            
            <Button Clicked="TakePicture" Text="Foto"></Button>
            <Label Text="Faces: " FontAttributes="Bold" FontSize="20"  
                        HorizontalOptions="CenterAndExpand"/>
            
            <ListView x:Name="FacesListView"
                      IsPullToRefreshEnabled="true"
                      CachingStrategy="RecycleElement">
                <ListView.ItemTemplate>
                    <DataTemplate>
                        <ViewCell>
                            <StackLayout>
                                <StackLayout Orientation="Horizontal" >
                                    <Label Text="Sexo:" FontAttributes="Bold"></Label>
                                    <Label Text="{Binding FaceAttributes.Gender}"></Label>
                                    <Label Text="Idade:" FontAttributes="Bold"></Label>
                                    <Label Text="{Binding FaceAttributes.Age}"></Label>
                                    <Label Text="Óculos:" FontAttributes="Bold"></Label>
                                    <Label Text="{Binding FaceAttributes.Glasses}"></Label>
                                </StackLayout>
                                <StackLayout Orientation="Horizontal" >
                                    <Label Text="Raiva:" FontAttributes="Bold"></Label>
                                    <Label Text="{Binding FaceAttributes.Emotion.Anger}"></Label>
                                    <Label Text="Felicidade:" FontAttributes="Bold"></Label>
                                    <Label Text="{Binding FaceAttributes.Emotion.Happiness}"></Label>
                                    <Label Text="Desprezo:" FontAttributes="Bold"></Label>
                                    <Label Text="{Binding FaceAttributes.Emotion.Contempt}"></Label>
                                    <Label Text="Surpreso:" FontAttributes="Bold"></Label>
                                    <Label Text="{Binding FaceAttributes.Emotion.Surprise}"></Label>
                                </StackLayout>
                            </StackLayout>
                        </ViewCell>
                    </DataTemplate>
                </ListView.ItemTemplate>
            </ListView>
        </StackLayout>
    </ScrollView>

</ContentPage>