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SimpleCaptcha(2) is the simplest and a robust captcha plugin. Its implementation requires adding up a single line in views and in controllers/models. SimpleCaptcha2 is available to be used with Rails 3 + 4. This is a fork of the popular Rubygem simple_captcha which got abandoned.


  • Zero FileSystem usage (secret code moved to db-store and image storage removed).
  • Provides various image styles.
  • Provides three level of complexity of images.
  • Works absolutely fine in distributed environment(session and db based implementation works fine in distributed environment).
  • Implementation is as easy as just writing a single line in your view. <%= show_simple_captcha %> within the 'form' tags.
  • Flexible DOM and CSS handling(There is a separate view partial for rendering SimpleCaptcha DOM elements).
  • Automated removal of 1 hour old unmatched simple_captcha data.



You might need to install Ghostscript on a Mac-System or a Debian-System:

brew install ghostscript
apt-get install ghostscript

The default font, that imagemagick uses is Arial. Make sure that font is available (apt install ttf-mscorefonts-installer) or change the font in the SimpleCaptcha config.

Put this into your Gemfile

gem 'simple_captcha2', require: 'simple_captcha'

and run bundle install.


After installation, follow these simple steps to setup the plugin. The setup will depend on the version of rails your application is using.

rails generate simple_captcha [template_format] # Available options erb, haml. Default: erb
rake db:migrate # Mongoid: skip this step and remove the migration


There are two usage scenarios:

Controller Based

Add the following line in the file "app/controllers/application.rb"

ApplicationController < ActionController::Base
  include SimpleCaptcha::ControllerHelpers

In the view file within the form tags add this code

<%= show_simple_captcha %>

and in the controller's action authenticate it as

if simple_captcha_valid?
  do this
  do that

Model Based

This is suggested, if you want to integrate the error message into the normal form validation flow.

In the view file within the form tags write this code

<%= show_simple_captcha(:object=>"user") %>

and in the model class add this code

class User < ActiveRecord::Base


class User
  include SimpleCaptcha::ModelHelpers

Strong parameters (Rails 4.x)

Must add them:

:captcha, :captcha_key

Form-Builder helper

<%= form_for @user do |form| -%>
  <%= form.simple_captcha :label => "Enter numbers.." %>
<% end -%>

Validating with captcha

NOTE: @user.valid? will still work as it should, it will not validate the captcha code.


Saving with captcha

NOTE: will still work as it should, it will not validate the captcha code.


Formtastic integration

SimpleCaptcha detects if you are using Formtastic:

<%= form.input :captcha, :as => :simple_captcha %>


You can make the Captcha always pass with a initializer file: config/initializers/simple_captcha.rb

SimpleCaptcha.always_pass = Rails.env.test?

You can also ask for the value, e.g. Acceptance Tests/Features:

visit '/pages/form_tag'
assert_equal 1, SimpleCaptcha::SimpleCaptchaData.count
fill_in 'captcha', with: SimpleCaptcha::SimpleCaptchaData.first.value

ORM support

simple-captcha2 supports 3 type of ORM: ActiveRecord, Sequel and Mongoid.

Selection of ORM is base on loaded classes. If ActiveRecord is loaded then it will be used for the simple captcha data model. If ActiveRecord is undefined, Sequel presence is tested. If Sequel is defined it will used for the simple captcha data model. If not, Mongoid is used.

For instance if your application is using Sequel as an ORM just make sure you require sequel-rails gem before simple-captcha2 in your Gemfile and respective model will be selected automatically.

Options & Examples

View Options

  • :label - provides the custom text b/w the image and the text field, the default is "type the code from the image"
  • :object - the name of the object of the model class, to implement the model based captcha.
  • :code_type - return numeric only if set to 'numeric'
  • :multiple - allow to use the same captcha in multiple forms in one page. True for the first appaerance and false for the rest.

Global options

  • :image_style - provides the specific image style for the captcha image. There are eight different styles available with the plugin as...
  1. simply_blue
  2. simply_red
  3. simply_green
  4. charcoal_grey
  5. embosed_silver
  6. all_black
  7. distorted_black
  8. almost_invisible

Default style is 'simply_blue'. You can also specify 'random' to select the random image style.

  • :distortion - handles the complexity of the image. The :distortion can be set to 'low', 'medium' or 'high'. Default is 'low'.

  • :implode - handles the complexity of the image. The :implode can be set to 'none', 'low', 'medium' or 'high'. Default is 'medium'.

Create "./config/initializers/simple_captcha.rb"

SimpleCaptcha.setup do |sc|
  # default: 100x28
  sc.image_size = '120x40'

  # default: 5
  sc.length = 6

  # default: simply_blue
  # possible values:
  # 'embosed_silver',
  # 'simply_red',
  # 'simply_green',
  # 'simply_blue',
  # 'distorted_black',
  # 'all_black',
  # 'charcoal_grey',
  # 'almost_invisible'
  # 'random'
  sc.image_style = 'simply_green'

  # default: low
  # possible values: 'low', 'medium', 'high', 'random'
  sc.distortion = 'medium'

  # default: medium
  # possible values: 'none', 'low', 'medium', 'high'
  sc.implode = 'low'

You can add your own style:

SimpleCaptcha.setup do |sc|
  sc.image_style = 'mycaptha'
  sc.add_image_style('mycaptha', [
      "-background '#F4F7F8'",
      "-fill '#86818B'",
      "-border 1",
      "-bordercolor '#E0E2E3'"])

You can provide the path where image_magick is installed as well:

SimpleCaptcha.setup do |sc|
  sc.image_magick_path = '/usr/bin' # you can check this from console by running: which convert

You can setup in which format the reload of the captcha is executed:

SimpleCaptcha.setup do |sc|
  sc.refresh_format = :prototype # or :jquery, or :plain_javascript default is :jquery

If needed, you can explicitly state the font used for generating the captcha:

SimpleCaptcha.setup do |sc|
  sc.font = "DejaVu-Sans"

How to change the CSS for SimpleCaptcha DOM elements?

You can change the CSS of the SimpleCaptcha DOM elements as per your need in this file.


View's Examples

Controller Based Example

<%= show_simple_captcha %>

<%= show_simple_captcha(:label => "human authentication") %>

Model Based Example

<%= show_simple_captcha(:object => 'user', :label => "human authentication") %>

Model Options

  • :message - provides the custom message on failure of captcha authentication the default is "Secret Code did not match with the Image"

  • :add_to_base - if set to true, appends the error message to the base.

Model's Example
class User < ActiveRecord::Base

class User < ActiveRecord::Base
  apply_simple_captcha :message => "The secret Image and code were different", :add_to_base => true


    placeholder: "Enter the image value"
    label: "Enter the code in the box:"
    refresh_button_text: "Refresh"
      default: "Secret Code did not match with the Image"
      user: "The secret Image and code were different"


For testing, generate a temporary Rails dummy app inside test:

bundle exec rake dummy:setup
bundle exec rake app:db:migrate
bundle exec rake app:db:migrate RAILS_ENV=test
bundle exec rake test

Please add test cases when adding new functionality. I started with some basic example integration tests for a very basic coverage.

The tests will be run on Travis-CI.

Who's who?

Enjoy the simplest captcha implementation.

Original Author of the Version for Rails 2: Author: Sur, Blog:, Contact: Plugin Homepage:

Plugin update for rails 3:

update for Rails 4, tests and forked by Stefan Wienert (pludoni GmbH)


Rails 3+4 support now! Simple Captcha is the simplest and a robust captcha plugin. Its implementation requires adding up a single line in views and in controllers/models.





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