Detect checkboxes using openCV

First we find all closed contours using findContours and then checking on hierarchy if it has a chield hierarchy[i][2] != -1 After that we check if the child hierarchy has a sibling (otherwise it's just the internal contour and the contour is not filled) firtstChildHierarchy = hierarchy[hierarchy[i][2]] isFilled = firtstChildHierarchy[0]!=-1 After that we check if it resembles a box by having 2 sets of parallel lines perpendicular with each other