Web Development

  Homes arrow Web Development arrow Page 2 - The Trouble with CAPTCHA
 Webmaster Tools
Base64 Encoding 
Browser Settings 
CSS Coder 
CSS Navigation Menu 
Datetime Converter 
DHTML Tooltip 
Dig Utility 
DNS Utility 
Dropdown Menu 
Fetch Content 
Fetch Header 
Floating Layer 
htaccess Generator 
HTML Encoder 
HTML Entities 
IP Convert 
Meta Tags 
Password Encryption
Password Strength
Pattern Extractor 
Ping Utility 
Pop-Up Window 
Regex Extractor 
Regex Match 
Scrollbar Color 
Source Viewer 
Syntax Highlighting 
URL Encoding 
Web Safe Colors 
Forums Sitemap 
Weekly Newsletter
Developer Updates  
Free Website Content 
 RSS  Articles
 RSS  Forums
 RSS  All Feeds
Write For Us 
Contact Us 
Site Map 
Privacy Policy 
  >>> SIGN UP!  
  Lost Password? 

The Trouble with CAPTCHA
By: Bruce Coker
  • Search For More Articles!
  • Disclaimer
  • Author Terms
  • Rating: 5 stars5 stars5 stars5 stars5 stars / 3

    Table of Contents:
  • The Trouble with CAPTCHA
  • Alternatives to CAPTCHA
  • More Alternatives

  • Rate this Article: Poor Best 
      Del.ici.ous Digg
      Blink Simpy
      Google Spurl
      Y! MyWeb Furl
    Email Me Similar Content When Posted
    Add Developer Shed Article Feed To Your Site
    Email Article To Friend
    Print Version Of Article
    PDF Version Of Article




    The Trouble with CAPTCHA - Alternatives to CAPTCHA

    (Page 2 of 4 )

    While there may be little that can be done to prevent circumvention by human operators, a variety of attempts have been made to implement CAPTCHA-like puzzles that are less vulnerable to machine-based compromise.

    Image Recognition

    Image recognition in its simplest form requires users to recognize images rather than letters in order to solve the challenge. These images can be computer generated, but a better system involves the use of photographs, as these are easy for humans to decipher but highly challenging for computers.

    One example of how this works is by users being asked a question and having to select from a list the number of images that represent the correct answer. Kittenauth is one such system. It presents an array of cute cat and kitten pictures alongside images of a whole range of other animals such as elephants, hedgehogs, pandas and horses. The challenge is simple enough: click on the pictures that contain kittens and hit the submit button.

    The Kittenauth system: just click the kittens

    The principle at work here is that it's straightforward for a human to distinguish a kitten from some other cute furry animal, but very difficult for a computer to do the same. As a secondary benefit, kittens are much cuter to look at than illegibly distorted letters, so users are less likely to become annoyed by the challenge. Of course the images could easily vary to reflect a particular site's content: a clothing site, for example, could ask its users to pick out dresses but ignore the suits and shoes.

    On the face of it, this sounds like the ideal solution. However, it does have certain drawbacks, the main one being accessibility. While traditional captures could be delivered as sound files, this is harder to accomplish with photographs, and easier for a bot to decipher, making use of the kittenauth system almost impossible for the visually impaired. Some copycat systems have attempted to resolve this with the use of alt tags to describe the images, but this is self-defeating, as plain text is trivial for a computer to parse.

    A second challenge to the photograph-based system is the need to separate the images from their filenames, as access to these would allow the solution to be reverse engineered. The images must therefore be streamed in real time from a database with no repeating identifiers.

    The system is also potentially vulnerable to brute force cracking, either by repeated random attempts or by image "harvesting" in which a bot gathers the images from a particular database, learning over time which are kittens and then using this knowledge to break the system. A successful workaround for this has been to introduce multiple sets of images, so instead of always selecting kittens you might variously have to identify motor bikes, airplanes or power tools. The wider the range of possible passing sets, the more difficult the system becomes to break.

    More Web Development Articles
    More By Bruce Coker



    - On Page SEO for New Domains
    - Improve Your Site`s Speed
    - Safari Books Online Review
    - Creating an Estore From the Ground Up
    - Most Common SEO Mistakes Developers Make
    - Making the Most of Your Titles and Meta Desc...
    - Five Ways Using Flash Can Damage Your Site
    - A Web Designer`s Guide to Colors
    - Use Webstarts to Create a Free Site
    - More Than Just Looks. How Your Web Design C...
    - How to Design Content Pages
    - Mint Review
    - Make Your WordPress Website Look Professional
    - How to Create a Mobile Web Site
    - Meta Tags: Still Useful?

    Developer Shed Affiliates


    © 2003-2019 by Developer Shed. All rights reserved. DS Cluster - Follow our Sitemap