title: free form image selection (preferably in c++)
body: <p>I am new to image manipulation. I have noticed that you can specify a <a href="http://nashruddin.com/OpenCV_Region_of_Interest_%28ROI%29" rel="noreferrer">rectangular region of interest</a> and others like <a href="http://nashruddin.com/OpenCV_Circular_ROI" rel="noreferrer">circles</a> etc in image manipulation libraries like opencv. Basic paint programs like ms-paint incorporate free form selection but i cannot seem to find a function or tutorial on how to do free form image selection in opencv or other image processing libraries. Any ideas on how to achieve this?
  PS:  My preferred language is c/c++.
  <img src="https://i.stack.imgur.com/x5g4G.jpg" alt="enter image description here"></p>