How to Solve Simple Captchas using Python Tesseract

 

CAPTCHA stands for Completely Automated Public Turing test to tell Computers and Humans Apart. As the acronym suggests, it is a test used to determine whether the user is human or not. A typical captcha consists of a distorted test, which a computer program cannot interpret but a human can (hopefully) still read.

This tutorial will show you how to bypass simple captchas using an OCR in Python.

What is an OCR?

Optical Character Recognition, or OCR, is the recognition of printed or written characters by a computer. It enables you to convert different types of documents, such as scanned paper documents, PDF files or images captured by a digital camera into editable and searchable data.

Popular open source OCR tools are Tesseract, GOCR and Ocrad. We will use Tesseract for this tutorial.

Tesseract

Tesseract is an open source OCR engine for various operating systems. It’s considered one of the most accurate OCR engines currently available, with the precision depending on the clearness of the image. Google has sponsored its development since 2006.

PyTesseract

Python-Tesseract is a python wrapper that helps you use Tesseract-OCR engine to convert images to the accepted format from Python. It can read all image types – png, jpeg, gif, tiff, bmp, etc.

Using Tesseract to solve a simple Captchas

Tesseract is designed to read regular printed text. If we want to use Tesseract effectively, we will need to modify the captcha images to remove the background noise, isolate the text and then pass it over to Tesseract to recognize the captcha.

Below are the package requirements for this tutorial in python.

  • Python 3.0 ( https://www.python.org/downloads/ )
  • PIP to install the following packages in Python ( https://pip.pypa.io/en/stable/installing/)
  • Tesseract-OCR, installation instructions for Tesseract are available at (https://github.com/tesseract-ocr/tesseract/wiki)
  • PyTesseract,  requires Python Imaging Library(PIL) and python version 2.5 or later. To install it use pip install pytesseract
  • Python Imaging Library (PIL) , for adding image processing capabilities to your Python interpreter and to support library formats. Install it using pip install pil
  • ImageMagic Tools  for processing and resampling image. Find the install instructions here https://www.imagemagick.org/script/download.php

    To know more about how to install PyTesseract with Tesseract, read here.

    For this tutorial, we will show you how to solve captchas. If the captchas we are trying to interpret are not difficult or messy we can make use of PyTesseract to bypass the captcha.

    As an example we will use the following captcha image

    After resampling, the image will look like this:

    captcha-after-resampling

    Code

    The script below can recognize the captcha and read the captcha image.

    If the embed above does not work you can download the script from this link.

    The script is named captcha_resolver.py. To run this script in command prompt or terminal you must type in the script name followed by the name of the captcha image as shown below.

    python captcha_resolver.py cap.jpg

    This will give the output as

    Resolving Captcha
    Resampling the Image
    ('Extracted Text', 'Viearer')

    This code can resolve simple captchas with sufficient clarity like the one we have just shown above. Let us know in the comments how this script worked for you or if you have a better solution.

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    Posted in:   Scraping Tips, Web Scraping Tutorials

    Responses

      Vasista Reddy October 24, 2018

      Since all the pixels in the pic are either white or black, you can use “OPENCV” to find the contours and draw them on the blank image with black pixels and then follow the above steps

      Reply

    Seb Tota January 3, 2019

    Hey guys I was wondering if you could help me out with this. I get an error:

    usage: captcha_resolver.py [-h] path
    captcha_resolver.py: error: too few arguments

    Reply

      Seb Tota January 3, 2019

      Never mind. I have to learn to read directions more carefully. Thank you so much!

      Reply

    Comments or Questions?

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