How to remove those pixels around the dates and watermark

Python
2

This is the code I have tried.

import cv2
import numpy as np

img = cv2.imread("mc.jpeg")
img = cv2.cvtColor(img, cv2.COLOR_BGR2GRAY)

alpha = 3.5
beta = -2

new = alpha * img + beta
new = np.clip(new, 0, 255).astype(np.uint8)

cv2.imwrite("cleaned.png", new)

Is there an adaptive way to adjust alpha and beta values for different images?

I have to use different alpha and beta values since not all images have the same contrast and/or brightness.