It's a Rails Captcha Engine for Rails 3 applications.

A captcha verification approach for Rails apps, directly integrated into ActiveRecord’s validation mechanism and providing helpers for ActionController and ActionView.

Due to many unrequited complaints to the recaptcha team with regard to its unreadability for real human users, this gem offers a more readable selection of captcha images.

AntiCaptcha api ruby wrapper

Metabypass | Ruby-based easy implementation for solving any type of captcha by Metabypass

This version include two important page 'Contact' and 'Register' with the 'Math-Captcha' method submit for prevent hacker attack.

Helps humankind with simpler captchas

HumanDetector is a friendly logic captcha for Rails the doesn't require any external system dependency (e.g. external captcha API connections). It uses a simple question that any 7 or more years old human can understand, but that a spambot will not be able to answer. This Gem supports Ruby v1.9.2...

Forked from https://github.com/kares/simple_captcha

This is a gem wrapper for tiny captcha in C with no dependencies.

IQ, Math Captcha

Simple lib to generate a math_captcha to prevent spammers in form. Supports localization.

Quick little arithmetic plain-text captcha

create captcha for api based project

Description of TinyCaptcha.

NO LONGER MAINTAINED AND NOT RECOMMENDED, AS BOTS ARE ABLE TO RESOLVE CAPTCHAS BETTER THAN HUMANS. Based on Login Attempts check if captcha is necessary. It stores a permanent cookie and uses a table for tracking login requests.

Implementation of captcha (Completely Automated Public Turing-Test to Tell Computers and Humans Apart) that is both easy to use and easy to customize/extend.

MVC based Math, Logic Captcha

Merb plugin that provides resource access rate limits and captcha'ing

Gem that uses RuCaptcha API to solver any type of captcha