How can I detect image artifacts?

Question

I need to make the script that will return True if image contains visual artifacts that look like gray clusters of pixels

Kind of artifact that I want to catch

Image I use as a sample

For now the best idea that I've got is to create a mask for the the range of hsv shades, count non-zero values and compare this amount to the similar amount of the sample-picture without the artifacts:

corrupted = cv2.imread("001.jpg")
sample = cv2.imread("002.jpg")

hsv_min = np.array((0, 0, 0), np.uint8)
hsv_max = np.array((179, 7, 255), np.uint8)

hsv = cv2.cvtColor(corrupted, cv2.COLOR_BGR2HSV)
hsv2 = cv2.cvtColor(sample, cv2.COLOR_BGR2HSV)

thresh = cv2.inRange(hsv, hsv_min, hsv_max)
thresh2 = cv2.inRange(hsv2, hsv_min, hsv_max)

nz = cv2.countNonZero(thresh)
nz2 = cv2.countNonZero(thresh2)

if nz > nz2:
  print(True)

I want to know if there is a specific tool for that or maybe the more convenient and efficient way to do that with opencv.