Here, bounding rectangle is drawn with minimum area, so it considers the rotation also. The function used is cv.minAreaRect(). It returns a Box2D structure which contains following details - ( center (x,y), (width, height), angle of rotation ). But to draw this rectangle, we need 4 corners of the rectangle. It is obtained by the function cv.boxPoints()
rect = cv.minAreaRect(cnt)
box = cv.boxPoints(rect)
box = np.int0(box)
cv.drawContours(img,[box],0,(0,0,255),2)Both the rectangles are shown in a single image. Green rectangle shows the normal bounding rect. Red rectangle is the rotated rect.
https://docs.opencv.org/3.4/dd/d49/tutorial_py_contour_features.html
OBB BOUNDING BOX → GET ANGLE BOUNDING BOX → ROTATE