Decoding CAPTCHAs. C Word 2003 Selection.Find.Execute. Most people dont know this but my honors thesis was about using a computer program to read text out of web images. My theory was that if you could get a high level of successful extraction you could use it as another source of data which could be used to improve search engine results. I was even quite successful in doing it, but never really followed my experiments up. Super Sonic Mugen Char. My honors adviser Dr Junbin Gao http csusap. I should write some form of article on what I had learnt. Well I finally got around to doing it. While what follows is not exactly what I was studying it is something I wish had existed when I started looking around. AJAX Form with CAPTCHA, Realtime Validation and PHP Backend. Last updated on February 7th, 2016 by Gabriel Livan 559 Comments. ASP. NET Captcha Control details. Java Captcha Library details. PHP Captcha Library details. ASP Captcha Component details. Why BotDetect BotDetect Captcha vs. CSS Form Styling. Pure CSS radios, checkboxes, selects, file upload, date picker, tooltips, and even google captcha Tweet. Search Engine Rankings offer 100 FREE, instant, online reports of the top 10 webpage rankings in the top 3 search engines Google, Bing and YahooLegal StuffDisclaimer. I am posting this article solely for information and educational purposes. I do not condone the use or act of ethical or unethical hacking nor circumvention of copy protection etc The use of this code for any unethical or illegal purposes is not condoned by myself nor any other persons mentioned in this article. This work is licenced under a Creative Commons Licence. So as I mentioned essentially what I attempted to do was take standard images on the web, and extract the text out them as a way of improving search results. Interestingly I based most of my researchideas by looking at methods of cracking CAPTCHAs. A CAPTCHA as you may well know is one of those annoying Type in the letters you see in the image above things you see on many website signup pages or comment sections. Captcha For Php Free Download' title='Captcha For Php Free Download' />A CAPTCHA image is designed so that a human can read it without difficulty while a computer is unable to. This in practice has never really worked with pretty much every CAPTCHA that is published on the web getting cracked within a matter of months. Knowing this my theory was that since people can get a computer to read something that it shouldnt be able to, then normal images such as website logos should be much easier to break using the same methods. I was actually surprisingly successful in my goal with over 6. I used in my sample set. Rather high considering the variety of different images that are on the web. What I did find however while doing my research was a lack of sample code or applications which show you how to crack CAPTCHAs. While there are some excellent tutorials and many published papers on it they are very light on algorithms or sample code. In fact I didnt find any beyond some non working PHP scripts and some Perl fragments which strung together a few non related programs and gave some reasonable results when presented with very simple CAPTCHAs. None of them helped me very much. I found that what I needed was some detailed code with examples I could run and tweak and see how it worked. I think I am just one of those people that can read the theory, and follow along, but without something to prod and poke I never really understand it. Most of the papers and articles said they would not publish code due the potential for miss use. Personally I think it is a waste of time since in reality building a CAPTCHA breaker is quite easy once you know how. So because of the lack of examples, and the problems I had initially getting started, I thought I would put together this article with full detailed explanations working code showing how to go about breaking a CAPTCHA. Lets get started. Free scripting and prototyping environment program for 3D object behavior. Runs on Windows 9598NT. Reads many common 3D file formats. Here is a list in order of things I am going to discuss. Technology used. All of the sample code is written in Python 2. Python Image Library. It will probably work in Python 2. I had installed. To get started just install Python then install the Python Image Library. Prefix. I am going to hardcode a lot of the values in this example. I am not trying to create a general CAPTCHA solver, but one specific to the examples given. This is just to keep the examples short and concise. CAPTCHAs, What are they Anyway A CAPTCHA is basically just an implementation of a one way function. This is a function where it is easy to take input and compute the result, but difficult to take the result and compute the input. What is different about them though is that while they are difficult for a computer to take the result and output the inputs, it should be easy for a human to do it. A CAPTCHA can be thought of in simple terms as a Are you a human test. Essentially they are implemented by showing an image which has some word or letters embedded in it. They are used for preventing automated spam on many online websites. An example can be found on the Windows Live ID signup page https signup. MBI wreplyhttp 2. F2. Fmail. live. Fdefault. GB bk1. 24. You display the image, the human decodes the text in it and enters it into the form. A simple idea which seems like a good solution to the problem of a computer coming along signing up for thousands of spam email accounts or posting thousands of threads in your forum trying to sell viagra. The problem is that AI, in particular image recognition techniques have evolved and become very effective in certain areas. OCR Optical Character Recognition is pretty accurate these days and can easily read printed text. The solution was to add lines and colours and generally mess up the text in the image you are asking the human to decode to try and confuse the program. Basically what you have here is an arms race, and like every other arms race arms generally beat armour. Defeating a CAPTCHA which has been obscured is a little more difficult but still not impossible. Plus the image being generated cannot be too crazy or the human will not be able to read them. The above image is an example of the CAPTCHA we are going to decode. This is a live CAPTCHA posted on an actual website and not just a test image I have created. It is a very simple CAPTCHA, consisting of text which is a uniform size and colour against a white background with some noise pixels, colours, lines thrown in. You might think that such a CAPTCHA is difficult to decode because of this noise, however I will show that it can easily be removed. This CAPTCHA while not very strong is a good example of home coded CAPTCHAs which exist on the web. How to identify text in imagesHow to extract text in images. Many methods exist for identifying where text lives in an image and extracting it. A simple Google search will list thousands of articles which have new techniques and algorithms for identifying text. Examples include using image filters which blur the image horizontally and look for darker areas because the blur causes the text to be highlighted. Edge detection filters which just leave the outline of text, pattern detection, colour extraction etc For the purposes of this example I am going to use colour extraction. The reason for this is that it is a simple technique which I have had a lot of success in. Its the technique I used for my thesis which produced quite good results. The algorithm I am going to use against our example CAPTCHA is known as multivalued image decomposition. Essentially it is means is that we first build a histogram of colours in the image. This is done by taking all of the pixels, grouping them by colour and counting each group. Looking at our example you can see that means there will be about three main colours which will be quite common, either the background white the noise lines grey or the text red. Doing this in Python is very easy. The following code will open an image, convert it to a GIF makes things easier since it has 2. PIL import Image. Image. opencaptcha.