reCAPTCHA was too much for us, so we created this. Simplest captcha ever.

SimpleCaptcha is available to be used with Rails 3 + 4 or above and also it provides the backward compatibility with previous versions of Rails.

anti-captcha is a Ruby library for recognize captcha on anti-captcha.com

Simple gem to add captcha or negative captcha to your Rails 3 application

DeathByCaptcha allows you to solve captchas with manual labor

SimpleCaptcha is the simplest and a robust captcha. Its implementation requires adding up a single line in views and in controllers/models. SimpleCaptcha is available to be used with Rails2.0 or above and also it provides the backward compatibility with previous versions of Rails.

A captcha solver (only for easy ones) gem

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

A Google-style captcha for enterprise Rails apps

A Google-style captcha for enterprise Rails apps

ReCaptcha implements view helpers to generate ReCaptcha code, with the noscript counterpart, required methods that interface with the HTTP API for captcha verification, a DSL to generate a before_filter and the code to implement AJAX captcha validation.

Simple reverse captcha solution that consist in create a hidden field that should be always empty.

RedisCaptcha provides simple captcha that can be read by human.

MVC based Math, Logic Captcha

A simple image captcha gem

RMagickCaptcha is a gem that implements captcha for using in Rails application.

Simple, easy captcha for Sinatra

Gem that uses RuCaptcha API to solver any type of captcha

A simple and custom captcha for Rails3.

Death by Captcha Ruby implementation (HTTP API)