I have a image i need to read the black color of image and change the black to some text using unity

I am working on project where i am getting the webcam texture and clicking the photo and converting the image to black and white using threshold. I want the black area to be filled with text like the image below :

The code below shows how I am capturing the image and using the threshold value to have the black and white effect. The last lines are used to save the captured image on the disk.

     Texture2D photo = new Texture2D(webCamTexture.width , webCamTexture.height);
     photo.SetPixels(webCamTexture.GetPixels());
     photo.Apply();

     Mat imgMat = new Mat(photo.height, photo.width, CvType.CV_8UC1);
     Utils.texture2DToMat(photo, imgMat);
     Debug.Log("imgMat.ToString() " + imgMat.ToString());

     Imgproc.threshold(imgMat, imgMat, 100 , 200, Imgproc.THRESH_BINARY | Imgproc.THRESH_OTSU); 
     
     Texture2D texture = new Texture2D(imgMat.cols(), imgMat.rows(), TextureFormat.RGBA32, false);
     Utils.matToTexture2D(imgMat, texture);

     byte[] bytes = texture.EncodeToJPG();
     File.WriteAllBytes(path + _CaptureCounter.ToString() + ".jpg", bytes);

Here is the current result with the above code:

Thank you in advance for your help