need to find a way for polyp detection in a 2D image using OpenCV

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I am currently learning OpenCV. I am using OpenCV to perform segmentation and object detection in 2D images. I need to find a way to detect polyps in the intestines.Refer the pic below:-

I used object detection but that would need a template and one the disadvantages is that the template wont be rotated or scaled to check whether there are any similar copies in the source image. So i'm trying to find a new way to detect these polyps.I would be grateful if anyone of you could help me with this.