title: Simple pattern recognition from paper: knowledge test
body: <p>I want to make an app for test validation (on paper) with the camera (ex. android). Accordingly, I need to recognize filled response options on a paper, which I will do in advance.</p>
  
  <p>Prompt, where to start? Where to dig? 
  I know of the existence of the library OpenCV - it will help me? </p>
  
  <p>Thank you.</p>