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I solved problem. There are no noises.

#!/usr/bin/python37
#Raspberry pi 3/3B+/4B, OpenCV 4.2.0, Thonny 3.7.3
#Date: 4h March, 2020

import cv2
import numpy as np

img = cv2.imread("zebra_lane.jpg")
gray = cv2.cvtColor(img, cv2.COLOR_BGR2GRAY)
blurred = cv2.GaussianBlur(gray,
                           (15, 15), 6)

ret, thresh = cv2.threshold(blurred,
                            180, 255,
                            cv2.THRESH_BINARY)

contours, hier = cv2.findContours(thresh.copy(),
                                  cv2.RETR_TREE,
                                  cv2.CHAIN_APPROX_SIMPLE)


for c in contours:
    # if the contour is not sufficiently large, ignore it
    if  cv2.contourArea(c) < 2000:
        continue

    # get the min area rect
    rect = cv2.minAreaRect(c)
    box = cv2.boxPoints(rect)
    # convert all coordinates floating point values to int
    box = np.int0(box)
    # draw a red 'nghien' rectangle
    cv2.drawContours(img, [box], 0, (0, 0, 255), 2)
    cv2.imwrite('zebra_lane1.jpg', img)
    cv2.imshow("contours", img)

while True:
    key = cv2.waitKey(1)
    if key == 27:  
        break

cv2.destroyAllWindows()

Output: