Python.Opencv and slider captcha solution, can't recognize the right one among the same shapes?

Question

Python

Good day. I've been trying for a month to write a script for recognizing the captcha of the slider, this is a captcha where there is a slider and the puzzle needs to be moved into its "shadow" the script that I made recognizes the puzzle and its "shadow" and I need it to recognize only the shadow, how to do this?

Screenshot showing the script in action

Видите на скрине черный паззл ? мне нужное его распознать.

Here is my code:

import cv2
import numpy as np

img = cv2.imread("captcha.png")
hsv= cv2.cvtColor(img,cv2.COLOR_BGR2HSV)

lower_range = np.array([0,0,0])
upper_range = np.array([0,0,0])

mask = cv2.inRange(hsv,lower_range,upper_range)

contours,hierarchy = cv2.findContours(mask,cv2.RETR_EXTERNAL,cv2.CHAIN_APPROX_SIMPLE)

if len(contours) !=0:
    for contour in contours:
        if cv2.contourArea((contour)) > 500:
            x,y,w,h = cv2.boundingRect(contour)
            cv2.rectangle(img,(x,y),(x+w,y+h),(0,255,),1)
            print(x,':',y)
            my_file = open("coordinates.txt", "w")
            my_file.write(str(x)+":"+str(y))
            my_file.close()

#cv2.imshow("Image",img)
#cv2.imshow("Mask",mask)
cv2.waitKey(0)
cv2.destroyAllWindows()