Solving CTF captcha challenge by use ocr

[using pytesser]

from PIL import Image
from pytesser import *
import urllib2, urllib
 
def conn(url, post, header):
    post_data = {
        'answer': post
    }
    post = urllib.urlencode(post_data)
    request = urllib2.Request(url, post, header)
    res = urllib2.urlopen(request)
    return res.read()
 
 
def create_image_string(filename):
    im = Image.open(filename)
    return image_to_string(im)
 
 
def change_rgb(filename):
    im = Image.open(filename)
    im = im.convert('RGB')
    x, y = im.size
    im_pix = im.load()
    r, g, b = im_pix[0, 0]
 
    for i in range(x):
        for j in range(y):
            if im_pix[i, j] != (r, g, b):
                im_pix[i, j] = 0
            else:
                im_pix[i, j] = (255, 255, 255)
    im.save(filename)
 
 
if __name__ == "__main__":
    path = 'C:\\Users\\ohyt0\\PycharmProjects\\untitled1\\HCAMP\\captcha.png'
    url = 'http://debu.kr:53201/8671d960384a6dc7410701db14af4db2/'
    header = {
        'Cookie': 'CAPTCHA_GAME=1jccsarof6o2cr1vp0tlagjrh1;'
    }
    c = 0
 
    while 1:
        res = urllib2.Request(url, None, header)
        res = urllib2.urlopen(res).read()
        if res.find('data:image/png;base64,') == -1:
            print res
            break
 
        res = res[res.find("data:image/png;base64,") + len("data:image/png;base64,"):]
        res = res[:res.find("'>")]
        res = res.decode('base64')
 
        with open(path, "wb") as f:
            f.write(res)
 
        change_rgb(path)
        answer = create_image_string(path)[:-2]
 
        res = conn(url, answer, header)
        print str(c) + ' : ' + answer
 
        if res.find("Correct") != -1:
            print "Correct"
            c += 1
        else:
            c = 1
            print "Wrong"
 
#HCAMP{i_hate_captcha_chal13nge_TT}

[Using ocr library]

import urllib, urllib2
import base64, os
from PIL import Image
 
def check(answer):
    url = 'http://debu.kr:53201/8671d960384a6dc7410701db14af4db2/'
    params = {
        'answer': answer
    }
    headers = {
        'User-Agent': 'Mozilla/5.0',
        'Cookie': 'CAPTCHA_GAME=1jccsarof6o2cr1vp0tlagjrh1;'
    }
    req = urllib2.Request(url, urllib.urlencode(params).encode(), headers)
    res = urllib2.urlopen(req).read().decode("utf-8", "ignore")
    return "Correct" in res
 
 
def main():
    c = 1
    while True:
        url = 'http://debu.kr:53201/8671d960384a6dc7410701db14af4db2/'
        headers = {
            'User-Agent': 'Mozilla/5.0',
            'Cookie': 'CAPTCHA_GAME=1jccsarof6o2cr1vp0tlagjrh1;'
        }
        req = urllib2.Request(url, None, headers)
        res = urllib2.urlopen(req).read().decode("utf-8", "ignore")
        if res.find('data:image/png;base64,') == -1:
            print res
            break
 
        res = res[res.find("data:image/png;base64,") + len("data:image/png;base64,"):]
        res = res[:res.find("'>")]
        imgbin = base64.b64decode(res)
 
        f = open("temp.png", "wb")
        f.write(imgbin)
        f.close()
 
        img = Image.open("temp.png")
        img.save("temp.bmp")
 
        os.system("temp.exe")
 
        f = open("temp.txt", "rb")
        answer = f.read().decode()
        f.close()
 
        print str(c) + ' : ' + answer
        if check(answer):
            print "Correct"
            c += 1
        else:
            c = 1
            print "Wrong"
 
 
if __name__ == '__main__':
    main()

이번에 갔었던 17회 해킹캠프에서 출제한 Captcha 문젠데 그때는 위에있는 코드로 플래그를 얻었고 나중에 CTF가 끝나고 다른 ocr 라이브러리 이용해서 문제 푸셨다는 분이 코드를 올려주셔서 좀만 수정해서 사용하였다.

확실히 아래있는 코드가 정확성이 좋다.