How I can get a real height of contour in C#?

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C#

image-processing

I want to get the height of the tower inside the image. I measured it by the rule I found it 9 cm. I use contour to do the segmentation then I computed the height of contour but the output of my program is 358.
what is it? and how I get the real result?

What I have tried:

temp = new Image<Bgr, byte>("F:\\project\\brige1.png");

            Image<Gray, byte> img3 = temp.Convert<Gray, byte>().ThresholdBinary(new Gray(50), new Gray(255)).Dilate(1).Erode(1);

            Emgu.CV.Util.VectorOfVectorOfPoint contours = new Emgu.CV.Util.VectorOfVectorOfPoint();
            Mat m = new Mat();
            CvInvoke.FindContours(img3, contours, m, Emgu.CV.CvEnum.RetrType.External, Emgu.CV.CvEnum.ChainApproxMethod.ChainApproxSimple);
            Dictionary<int, double> dict = new Dictionary<int, double>();
            if (contours.Size > 0)
            {
                for (int i = 0; i < contours.Size; i++)
                {

                    Rectangle rect = CvInvoke.BoundingRectangle(contours[i]);
                    double aera = CvInvoke.ContourArea(contours[i]);

                    int h = rect.Height;

                    MessageBox.Show("The heith is = " + h.ToString());

                    CvInvoke.Rectangle(temp, rect, new MCvScalar(0, 255, 0), 3);


                    pictureBox5.Image = temp.Bitmap;

                    
                }