Captcha preprocessing and solving with Opencv and pytesseract

Problem

I am trying to write code in Python for the Image preprocessing and recognition using Tesseract-OCR. My goal is to solve this form of captcha reliably.

Original captcha and result of each preprocessing step

Steps as of Now

1. Greyscale and thresholding of image

2. Image enhancing with PIL

3. Convert to TIF and scale to >300px

4. Feed it to Tesseract-OCR (whitelisting all uppercase alphabets)

However, I still get an rather incorrect reading (EPQ M Q). What other preprocessing steps can I take to improve accuracy? My code and additional captcha of similar nature are appended below.

similar captchas I want to solve

Code

import cv2
import pytesseract
from PIL import Image, ImageEnhance, ImageFilter
def binarize_image_using_opencv(captcha_path, binary_image_path='input-black-n-white.jpg'):
     im_gray = cv2.imread(captcha_path, cv2.IMREAD_GRAYSCALE)
     (thresh, im_bw) = cv2.threshold(im_gray, 85, 255, cv2.THRESH_BINARY)
     # although thresh is used below, gonna pick something suitable
     im_bw = cv2.threshold(im_gray, thresh, 255, cv2.THRESH_BINARY)[1]
     cv2.imwrite(binary_image_path, im_bw)

     return binary_image_path

def preprocess_image_using_opencv(captcha_path):
     bin_image_path = binarize_image_using_opencv(captcha_path)

     im_bin = Image.open(bin_image_path)
     basewidth = 300  # in pixels
     wpercent = (basewidth/float(im_bin.size[0]))
     hsize = int((float(im_bin.size[1])*float(wpercent)))
     big = im_bin.resize((basewidth, hsize), Image.NEAREST)

     # tesseract-ocr only works with TIF so save the bigger image in that format
     tif_file = "input-NEAREST.tif"
     big.save(tif_file)

     return tif_file

def get_captcha_text_from_captcha_image(captcha_path):

     # Preprocess the image befor OCR
     tif_file = preprocess_image_using_opencv(captcha_path)



get_captcha_text_from_captcha_image("path/captcha.png")

im = Image.open("input-NEAREST.tif") # the second one 
im = im.filter(ImageFilter.MedianFilter())
enhancer = ImageEnhance.Contrast(im)
im = enhancer.enhance(2)
im = im.convert('1')
im.save('captchafinal.tif')
text = pytesseract.image_to_string(Image.open('captchafinal.tif'), config="-c 
tessedit_char_whitelist=ABCDEFGHIJKLMNOPQRSTUVWXYZ -psm 6")
print(text)