Using (C# , emgu library) how can I find deficit definition of bottle?

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C#

Visual-Studio

image

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Im want to find deficit on the bottle,using C#-EmguCV ,need to know the steps of image-prepossessing && select the deficit to calculation its area ..

My Input image:
1.jpg - Google Drive[^]

The needed Result
Output image showing where is the defect done by Matlab After image-prepossessing
2.jpg - Google Drive[^]

What I have tried:

As the below code i trying first to :
1-Convert image BGR-to-GRAY
2-Binarization thresholding (Making the background black)
3-Erode -->For Now the Result as image: 3.PNG - Google Drive[^]
AS you see the defected still in the image ,and this wrong because i cant using Masking on the image ..

I dont know the steps/Or what i do after Erode how can i put circle around the deficit
4-After that Masking...?

<pre>  Image<Bgr, byte> ImgInput;
        Image<Gray, byte> ImgGray;
        Image<Gray, byte> ImgBinariz;


        public Home()
        {
            InitializeComponent();
        }


        private void openToolStripMenuItem1_Click(object sender, EventArgs e)
        {
            try
            {
                OpenFileDialog ofd = new OpenFileDialog();

                if (ofd.ShowDialog() == DialogResult.OK)
                {
                    ImgInput = new Image<Bgr, byte>(ofd.FileName);// 3 dimension
                    ImgGray = ImgInput.Convert<Gray, byte>();//Convert BGR-GRAY
                    pictureBox1.Image = ImgGray.Bitmap;

                    //Binarization  thresholding
                    ImgBinariz = new Image<Gray, byte>(ImgGray.Width, ImgGray.Height, new Gray(0));//binay imge with black background
                    // pictureBox1.Image = ImgBinariz.Bitmap; //Make all the image black
                    CvInvoke.Threshold(ImgGray, ImgBinariz, 50, 255, ThresholdType.Otsu);

                     pictureBox1.Image = ImgBinariz.Erode(5).Bitmap;
                    //pictureBox1.Image = ImgBinariz.Bitmap;

                }

            }
            catch(Exception ex)
            {
                MessageBox.Show(ex.Message);
            }
        }