Need some suggestion about image processing

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Hello, need some suggestion about image processing to know whether it can be done using C /c++ as I am not familiar with MATLAB. I have attached one image. The arrow in the image show the indented circlular portion. I need to crop out only the portion inside the indented portion. I think there should be a sharp difference in gradient intensity in pixel at the indented portion. Is it possible to extract that portion out by reading the binary image?
Thanks in advance.

Have you looked at
http://cimg.sourceforge.net/index.shtml