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

Easy to use classical captcha for Rails apps

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

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.

NO LONGER MAINTAINED AND NOT RECOMMENDED, AS BOTS ARE ABLE TO RESOLVE CAPTCHAS BETTER THAN HUMANS.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.

To help with keep the bots at bay this gem helps you easily add honeypots to forms and/or obfuscate your form field names

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

0-9 arası sayıları kullanarak random olarak 2 sayı seçer ve yine random olarak toplama ya da çarpma yaparak sonucu verir.

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

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

Captcha based on encyrpting and decrypting user data by mathematical operation

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

Death by Captcha Ruby implementation (HTTP API)

Simple negative captcha for Rails

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.

Description of TinyCaptcha.

Antigate (Decode captcha service) wrapper for Ruby

Generates and verifies ascii art captcha.