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.FaceAddInPerson.cs

	    private async Task FaceAddInPerson(string image)
	    {
            
	        // Call the Face API.
	        try
	        {
	            using (Stream imageFileStream = File.OpenRead(image))
	            {
	                var result = await _faceServiceClient.AddPersonFaceAsync("grupo",personId, imageFileStream);

	                 faceId1 =  result.PersistedFaceId;

	            }

	            await _faceServiceClient.TrainPersonGroupAsync("grupo");
            }
	    // Catch and display Face API errors.
	    catch (FaceAPIException f)
	    {
	        await DisplayAlert("Error", f.ErrorMessage, "ok");
	    }
	    // Catch and display all other errors.
	    catch (Exception e)
	    {
	        await DisplayAlert("Error", e.Message, "ok");
	    }

        }