pyProcessDarkSpots

import cv2
def getDist(coord1, coord2):
    return ((coord1[0] - coord2[0]) ** 2 + (coord1[1] - coord2[1]) ** 2) ** 0.5

grayimg = cv2.imread("FourSpots.jpg", cv2.IMREAD_GRAYSCALE)
foundSpots = []                  # list of tuples of coordinates of top left corner of each dark spot
for row, aline in enumerate(grayimg):           # aline contains one horizontal line of pixels
    for col, pixel in enumerate(aline):         # pixel contains whiteness level of one pixel
        if pixel < 85:                          # Find a dark pixel
            for spot in foundSpots:
                if getDist((row, col), spot) < 50:
                    break                       # pixel is close to an already known spot
            else:
                foundSpots.append((row, col))      # Last loop did NOT end with break
baseDist = 0
num = len(foundSpots)
for x in range(num):            # Look at all combinations of 2 spots, and check their separation
    for y in range(x+1, num):
        d = getDist(foundSpots[x], foundSpots[y])
        if d > baseDist:
            baseDist = d                                    # keep the greatest distance
            basePair = (foundSpots[x], foundSpots[y])       # remember the base pair
otherSpots = [spot for spot in foundSpots if spot not in basePair]
pairs = ["A-C", "A-D", "B-C", "B-D"]
for i in basePair:
    for j in otherSpots:
        pc = (100 * getDist(i, j)) / baseDist
        print(f"{pairs.pop(0)} is {pc:.0f}% of A-B")

# Output:
# A-C is 81% of A-B
# A-D is 38% of A-B
# B-C is 44% of A-B
# B-D is 66% of A-B