img = cv2.resize(img, (0,0), fx=2, fy=2)

gray_img = cv2.cvtColor(img, cv2.COLOR_BGR2GRAY)
ret, thresh = cv2.threshold(gray_img, 127, 255, 1)
_, contours , _= cv2.findContours(thresh, cv2.RETR_TREE, 1)

cnt = contours
for i in range(len(contours)):

    #---- Mark contours above certain area ----
    if (cv2.contourArea(cnt[i]) > 1500):
        final_image = cv2.drawContours(img, cnt[i], -1, (0,255,0), 3)

cv2.imshow('Marked image', final_image )