废话不多说，首先nuget安装FaceRecognitionDotNet，其次下载models文件夹，链接https://github.com/ageitgey/face_recognition_models/
然后查找人脸数量和人脸比对程序如下：
public class facefind
{
private FaceRecognition FaceRecognition;
private Model model;
public facefind()
{
var path = Directory.GetCurrentDirectory();
FaceRecognition = FaceRecognition.Create(@"./models");
if (!Enum.TryParse<Model>("hog", true, out model))
{
Console.WriteLine($"\n\tmodel: cnn");
}
}

    public int findface(string url)
    {
        Uri imgUrl = new Uri(url);
        var webC = new System.Net.WebClient();
        try
        {
            Bitmap map = new Bitmap(webC.OpenRead(imgUrl));
            Console.WriteLine(map.Size);
            ;
            using (var unknownImage = FaceRecognition.LoadImage(map))
            {
                var faceLocations = FaceRecognition.FaceLocations(unknownImage, 2, model).ToList();
                return faceLocations.Count;

            }
        }
        catch(Exception e)
        {
            Console.WriteLine(e.Message);
            return 0;
        }
    }

    public bool compareface(string url,string comparurl)
    {
        Uri imgUrl = new Uri(url);
        Uri imgcmpareUrl = new Uri(comparurl);
        var webC = new System.Net.WebClient();
        Bitmap map = new Bitmap(webC.OpenRead(imgUrl));
        Bitmap mapcompare = new Bitmap(webC.OpenRead(imgcmpareUrl));
        var faceimage = FaceRecognition.LoadImage(map);
        FaceEncoding knownface = FaceRecognition.FaceEncodings(faceimage).First();
        var faceimage1 = FaceRecognition.LoadImage(mapcompare);
        FaceEncoding checkface = FaceRecognition.FaceEncodings(faceimage1).First();
        var result = FaceRecognition.CompareFace(knownface, checkface);
        return result;
    }
}

需要的同学拿去，在Ubuntu下dotnte restore 即可使用。
如果出现Gdip的错误，运行
1、apt-get install libgdiplus
2、cd /usr/lib
3、ln -s libgdiplus.so gdiplus.dll
即可解决。
如果在调试过程中出现问题的话可以私信我。