title: Crop and rotate picture OpenCV
body: <p>I am new in OpenCV so please to be lenient.
  I am doing an Android application to recognize the squares/rectangles and crop them.  Function which looks for the squares/rectangles puts the found objects to vector> squares. I just wonder how to crop the picture according to the data in points stored in vector> squares and how to compute an angle on which the picture should be rotated. Thank you for any help</p>