Class: ValidatesCaptcha::ImageGenerator::Simple

Inherits:
Object
  • Object
show all
Defined in:
lib/validates_captcha/image_generator/simple.rb

Overview

This class is responsible for creating the captcha image. It internally uses ImageMagick’s convert command to generate the image bytes. So ImageMagick must be installed on the system for it to work properly.

In order to deliver the captcha image to the user’s browser, Validate Captcha’s Rack middleware calls the methods of this class to create the image, to retrieve its mime type, and to construct the path to it.

The image generation process is no rocket science. The chars are just laid out next to each other with varying vertical positions, font sizes, and weights. Then a slight rotation is performed and some randomly positioned lines are rendered on the canvas.

Sure, the created captcha can easily be cracked by intelligent bots. As the name of the class suggests, it’s rather a starting point for your own implementations.

You can implement your own (better) image generator by creating a class that conforms to the method definitions of the example below.

Example for a custom image generator:

class AdvancedImageGenerator
  def generate(captcha_text)
    # ... do your magic here ...

    return string_containing_image_bytes
  end

  def mime_type
    'image/png'
  end

  def file_extension
    '.png'
  end
end

Then assign an instance of it to ValidatesCaptcha::Provider::DynamicImage#image_generator=.

ValidatesCaptcha::Provider::DynamicImage.image_generator = AdvancedImageGenerator.new
ValidatesCaptcha.provider = ValidatesCaptcha::Provider::DynamicImage.new

Or to ValidatesCaptcha::Provider::StaticImage#image_generator=.

ValidatesCaptcha::Provider::StaticImage.image_generator = AdvancedImageGenerator.new
ValidatesCaptcha.provider = ValidatesCaptcha::Provider::StaticImage.new

Constant Summary collapse

MIME_TYPE = 
'image/gif'.freeze
FILE_EXTENSION = 
'.gif'.freeze

Instance Method Summary collapse

Instance Method Details

#file_extension ⇒ Object

Returns the image file extension. This is always ‘.gif’.



89
90
91
 
# File 'lib/validates_captcha/image_generator/simple.rb', line 89

def file_extension
  FILE_EXTENSION
end

#generate(captcha_code) ⇒ Object

Returns a string containing the image bytes of the captcha. As the only argument, the cleartext captcha text must be passed.



58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
 
# File 'lib/validates_captcha/image_generator/simple.rb', line 58

def generate(captcha_code)
  image_width = captcha_code.length * 20 + 10

  cmd = []
  cmd << "convert -size #{image_width}x40 xc:grey84 -background grey84 -fill black "

  captcha_code.split(//).each_with_index do |char, i|
    cmd << " -pointsize #{rand(8) + 15} "
    cmd << " -weight #{rand(2) == 0 ? '4' : '8'}00 "
    cmd << " -draw 'text #{5 + 20 * i},#{rand(10) + 20} \"#{char}\"' "
  end

  cmd << "  -rotate #{rand(2) == 0 ? '-' : ''}5 -fill grey40 "

  captcha_code.size.times do
    cmd << "  -draw 'line #{rand(image_width)},0 #{rand(image_width)},60' "
  end

  cmd << "  gif:-"

  image_magick_command = cmd.join

  `#{image_magick_command}`
end

#mime_type ⇒ Object

Returns the image mime type. This is always ‘image/gif’.



84
85
86
 
# File 'lib/validates_captcha/image_generator/simple.rb', line 84

def mime_type
  MIME_TYPE
end