Spammer is flooding the Internet with many copies of the same message. And if we left our self unprotected then we can literally be overwhelmed by spam in a short period of time. but there is a solution CAPTCHA (Completely Automated Public Turing test to tell Computers and Humans Apart)  a challenge-response test most often placed within web forms to determine whether the user is human or a spammer.

There are hundred types of CAPTCHA available on the internet and everyone should use them according to their needs. In this article i have compiled a list of 12 best CAPTCHA services and script which will help you in your spam prevention.

1.Akismet:

Akismet filters out your comment and track-back spam for you, so you can focus on more important things. Akismet is a hosted web service that saves you time by automatically detecting comment and trackback spam. It’s hosted on their servers, but they give you access to it through plugins and API.

2.Asirra:

Asirra is a human interactive proof that asks users to identify photos of cats and dogs. It’s powered by over three million photos from their unique partnership with Petfinder.com. Protect your web site with  Asirra (Animal Species Image Recognition for Restricting Access) is a HIP that works by asking users to identify photographs of cats and dogs. This task is difficult for computers, but people can accomplish it quickly and accurately. Many even think it’s fun!

3.BotDetect:

BotDetect is unique among CAPTCHA solutions in offering many CAPTCHA image and sound styles. While each of them is easily comprehensible to human users, randomly using multiple CAPTCHA generation algorithms makes the CAPTCHA challenge practically impossible to pass automatically.

4.Captchas:


This server provides CAPTCHA images and audio files you can use in html-forms. Captchas images will prevent forms to be used by robots.

5.Captchator:


A CAPTCHA is a way to prevent automated web form submissions. You show the user an image with a confirmation code, and you only accept the submission if the user enters the code correctly. Captchator does exactly the same.

Features:

  • works with any web programming language and framework (PHP, Ruby/Rails, Python, ASP, Perl, …)
  • works on any server and shared hosting account, does not require extensions or special software
  • can be implemented in just a few lines of code
  • is easy to integrate with existing apps/websites

6.Cryptographp:

Cryptographp is a PHP script for generate CAPTCHA. Cryptographp limit the robots bombarding spams and automating the forms: spaces members subscriptions, guestbooks, forums… This script is free and does not use any database. It is compatible with PHP 4.3.0. Cryptographp also exists into plugins for WordPress, wpMu for WordPress, Symfony and Guppy.

7.Open CAPTCHA:


Open CAPTCHA is one of the best CAPTCHA solution for your website it has a lot of features.

Features:

  • It requires no special configurations or modules, it is a simple web service.
  • Basic installation is cut-and-paste, and requires no ability to program image manipuation scripts
  • New fonts, image algorithms, and distortions applied weekly.

8.ProCaptcha:

ProCaptcha is a form processor. It can work as a regular form, as a secure form, as a guest book, as an auto responder; it can collect testimonials. ProCaptcha can be easily hooked up to any form, protecting it from spam. ProCaptcha is developed for non-programmers. It doesn’t depend on the server’s platform. It is very flexible and offers a lot of features.

9.reCaptcha:

reCAPTCHA is a free CAPTCHA service that helps to digitize books, newspapers and old time radio shows. reCAPTCHA improves the process of digitizing books by sending words that cannot be read by computers to the Web in the form of CAPTCHAs for humans to decipher. More specifically, each word that cannot be read correctly by OCR is placed on an image and used as a CAPTCHA. This is possible because most OCR programs alert you when a word cannot be read correctly.

10.Securimage:

Securimage is an open-source free PHP CAPTCHA script for generating complex images and CAPTCHA codes to protect forms from spam and abuse. It can be easily added into existing forms on your website to provide protection from spam bots. It can run on most any web server as long as you have PHP installed, and GD support within PHP. Securimage does everything from generating the CAPTCHA images to validating the typed code. Audible codes can be streamed to the browser with Flash for the vision impaired.

11.Text Disguise;

Simply put, Text Disguise is a Human Interactive Proof. What is a Human Interactive Proof? It is a method of telling human users apart from computers (or, also known as “bots”). By presenting a CAPTCHA-image to a user, it requires that a living, breathing, thinking person be at the keyboard – interacting with your web site.

12.WebSpamProtect:


WebSpamProtect.com allows you to instantly add verification image (CAPTCHA) to your web site and protect your forms against spam robots. In order to protect your web form, our system requires that you install a small piece of code onto your web page. Our code requires that your web site support PHP, Perl, ASP or ASP.NET.