This example show how to building a Xamarin.Forms applications using Microsoft Cognitive Services to identify if two pictures are from same person - http://julianocustodio.com/face-verify

MainPage.xaml.cs

using System;
using Microsoft.ProjectOxford.Face;
using Plugin.Media;
using Plugin.Media.Abstractions;
using Xamarin.Forms;

namespace DemoFaceVerify
{
    public partial class MainPage : ContentPage
    {
        private readonly IFaceServiceClient _faceServiceClient;
        private readonly Guid personId;
        private Guid faceId1;
        private Guid faceId2;
        private string filePath1;

        public MainPage()
        {
            InitializeComponent();

            _faceServiceClient = new FaceServiceClient("KEY", "URL");

            faceId1 = new Guid();
            faceId2 = new Guid();
            personId = new Guid("PERSONID");
        }
    }
}