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

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

Easy to use classical captcha for Rails apps

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

A gem to generate captcha pictures.

NO LONGER MAINTAINED AND NOT RECOMMENDED, AS BOTS ARE ABLE TO RESOLVE CAPTCHAS BETTER THAN HUMANS.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

A Rails captcha gem that attempts to determine whether or not a user is human.

Captcha Client for YunPian.com

Tencent Cloud Ruby SDK is the official software development kit, which allows Ruby developers to write software that makes use of Tencent Cloud service CAPTCHA.

A simple and custom captcha for Rails3.

Google reCaptcha helpers and verifier

Rack middleware Captcha verification using Recaptcha API.

AntiCaptcha api ruby wrapper

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

Arithmetic Captcha

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

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

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

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