Unity Captcha is a gem that use two levels of Captcha. First level is about Left Hemisphere: Logic and Math. Second level is about Right Hemisphere: Intuition and Drawing. This two levels functioning in complete harmony creates unity and this is the base design of this Captcha.

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

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.

Easy to use classical captcha for Rails apps

A simple CAPTCHA implementation for Rails 5+ based on RMagick.

A gem to generate captcha pictures.

Captcha Client for YunPian.com

This library can help you create a captcha in your terminal application, which may be damaged by a large influx of requests.

Captcha-Plugin for Rails

This gem enable to use Captchme. Anti spam, Monetize captcha and Audience qualification

A simple and custom captcha for Rails3.

Google reCaptcha helpers and verifier

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

Implements view helpers for the ASIRRA CAPTCHA system for Rails-based websites

Captcha based on encyrpting and decrypting user data by mathematical operation

you will get arithmatic sum with answer you just have to compare with ur user in controller

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

Captcha Gem for Rails, which generates captcha image by Rust.

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.

A smart captcha library