Added file cache, can setup how many images you want generate by ,

RuCaptcha will use cache for next requests.
  When you restart Rails processes it will generate new again and clean the old caches.

lib/rucaptcha.rb

@@ -5,6 +5,7 @@ require_relative 'rucaptcha/version'
 require_relative 'rucaptcha/configuration'
 require_relative 'rucaptcha/controller_helpers'
 require_relative 'rucaptcha/view_helpers'
+require_relative 'rucaptcha/cache'
 require_relative 'rucaptcha/captcha'
 require_relative 'rucaptcha/engine'
 
@@ -13,19 +14,24 @@ module RuCaptcha
     def config
       return @config if defined?(@config)
       @config = Configuration.new
-      @config.len = 4
-      @config.width = 150
-      @config.height = 48
-      @config.implode = 0.4
+      @config.len         = 4
+      @config.width       = 150
+      @config.height      = 48
+      @config.implode     = 0.4
+      @config.cache_limit = 100
       @config
     end
 
     def configure(&block)
       config.instance_exec(&block)
+
+      # enable cache if cache_limit less than 1
+      if config.cache_limit >= 1
+        RuCaptcha::Captcha.send(:include, RuCaptcha::Cache)
+      end
     end
   end
 end
 
-
-ActionController::Base.send :include, RuCaptcha::ControllerHelpers
-ActionView::Base.send :include, RuCaptcha::ViewHelpers
+ActionController::Base.send(:include, RuCaptcha::ControllerHelpers)
+ActionView::Base.send(:include, RuCaptcha::ViewHelpers)

lib/rucaptcha/cache.rb

@@ -0,0 +1,44 @@
+module RuCaptcha
+  # File Cache
+  module Cache
+    extend ActiveSupport::Concern
+
+    included do
+      class << self
+        alias_method_chain :create, :cache
+        alias_method_chain :random_chars, :cache
+      end
+    end
+
+    module ClassMethods
+      def create_with_cache(code)
+        cache.fetch(code) do
+          create_without_cache(code)
+        end
+      end
+
+      def random_chars_with_cache
+        if cached_codes.length >= RuCaptcha.config.cache_limit
+          return cached_codes.sample
+        else
+          code = random_chars_without_cache
+          cached_codes << code
+          return code
+        end
+      end
+
+      def cache
+        return @cache if defined?(@cache)
+
+        cache_path = Rails.root.join('tmp', 'cache', 'rucaptcha')
+        @cache = ActiveSupport::Cache::FileStore.new(cache_path)
+        @cache.clear
+        @cache
+      end
+
+      def cached_codes
+        @cached_codes ||= []
+      end
+    end
+  end
+end

lib/rucaptcha/captcha.rb

@@ -2,44 +2,53 @@ require 'posix-spawn'
 
 module RuCaptcha
   class Captcha
-    def self.rand_color
-      r = rand(129).to_s(8).to_i
-      rgb = [rand(100).to_s(8), rand(100).to_s(8), rand(100).to_s(8)]
+    class << self
+      def rand_color
+        rgb = [rand(100).to_s(8), rand(100).to_s(8), rand(100).to_s(8)]
 
-      "rgba(#{rgb.join(',')},1)"
-    end
-
-    def self.create(code)
-      size = "#{RuCaptcha.config.width}x#{RuCaptcha.config.height}"
-      font_size = (RuCaptcha.config.height * 0.8).to_i
-      half_width = RuCaptcha.config.width / 2
-      half_height = RuCaptcha.config.height / 2
-      line_color = rand_color
-
-      chars = code.split('')
-      text_opts = []
-      text_top = (RuCaptcha.config.height - font_size) / 2
-      text_padding = 5
-      text_width = (RuCaptcha.config.width / chars.size) - text_padding * 2
-      text_left = 5
-      chars.each_with_index do |char, i|
-        text_opts << %(-fill '#{rand_color}' -draw 'text #{(text_left + text_width)  * i + text_left},#{text_top} "#{char}"')
+        "rgba(#{rgb.join(',')},1)"
       end
 
-      command = <<-CODE
-        convert -size #{size} #{text_opts.join(' ')}  \
-        -draw 'stroke #{line_color} line #{rand(10)},#{rand(20)} #{half_width + rand(half_width)},#{rand(half_height)}' \
-        -draw 'stroke #{line_color} line #{rand(10)},#{rand(25)} #{half_width + rand(half_width)},#{half_height + rand(half_height)}' \
-        -draw 'stroke #{line_color} line #{rand(10)},#{rand(30)} #{half_width + rand(half_width)},#{half_height + rand(half_height)}' \
-        -wave #{rand(2) + 2}x#{rand(2) + 1} \
-        -gravity NorthWest -sketch 1x10+#{rand(1)} -pointsize #{font_size} -weight 700 \
-        -implode #{RuCaptcha.config.implode} label:- png:-
-      CODE
-      command.strip!
-      # puts command
-      pid, stdin, stdout, stderr = POSIX::Spawn.popen4(command)
-      Process.waitpid(pid)
-      stdout.read
+      def random_chars
+        chars = SecureRandom.hex(RuCaptcha.config.len / 2).downcase
+        chars.gsub!(/[0ol1]/i, (rand(8) + 2).to_s)
+        chars
+      end
+
+      # Create Captcha image by code
+      def create(code)
+        size         = "#{RuCaptcha.config.width}x#{RuCaptcha.config.height}"
+        font_size    = (RuCaptcha.config.height * 0.8).to_i
+        half_width   = RuCaptcha.config.width / 2
+        half_height  = RuCaptcha.config.height / 2
+        line_color   = rand_color
+        chars        = code.split('')
+        text_opts    = []
+        text_top     = (RuCaptcha.config.height - font_size) / 2
+        text_padding = 5
+        text_width   = (RuCaptcha.config.width / chars.size) - text_padding * 2
+        text_left    = 5
+
+        chars.each_with_index do |char, i|
+          text_opts << %(-fill '#{rand_color}' -draw 'text #{(text_left + text_width) * i + text_left},#{text_top} "#{char}"')
+        end
+
+        command = <<-CODE
+          convert -size #{size} #{text_opts.join(' ')}  \
+          -draw 'stroke #{line_color} line #{rand(10)},#{rand(20)} #{half_width + rand(half_width)},#{rand(half_height)}' \
+          -draw 'stroke #{line_color} line #{rand(10)},#{rand(25)} #{half_width + rand(half_width)},#{half_height + rand(half_height)}' \
+          -draw 'stroke #{line_color} line #{rand(10)},#{rand(30)} #{half_width + rand(half_width)},#{half_height + rand(half_height)}' \
+          -wave #{rand(2) + 2}x#{rand(2) + 1} \
+          -gravity NorthWest -sketch 1x10+#{rand(1)} -pointsize #{font_size} -weight 700 \
+          -implode #{RuCaptcha.config.implode} label:- png:-
+        CODE
+
+        command.strip!
+        # puts command
+        pid, stdin, stdout, stderr = POSIX::Spawn.popen4(command)
+        Process.waitpid(pid)
+        stdout.read
+      end
     end
   end
 end

lib/rucaptcha/configuration.rb

@@ -1,5 +1,15 @@
 module RuCaptcha
   class Configuration
-    attr_accessor :width, :height, :font_size, :len, :implode
+    # Image width, default 150
+    attr_accessor :width
+    # Image height, default 48
+    attr_accessor :height
+    # Number of chars, default 4
+    attr_accessor :len
+    # implode, default 0.4
+    attr_accessor :implode
+    # Number of Captcha codes limit
+    # set 0 to disable limit and file cache, default: 100
+    attr_accessor :cache_limit
   end
 end

lib/rucaptcha/controller_helpers.rb

@@ -7,14 +7,8 @@ module RuCaptcha
     end
 
     def generate_rucaptcha
-      session[:_rucaptcha] = random_rucaptcha_chars
-      return RuCaptcha::Captcha.create(session[:_rucaptcha])
-    end
-
-    def random_rucaptcha_chars
-      chars = SecureRandom.hex(RuCaptcha.config.len / 2).downcase
-      chars.gsub!(/[0ol1]/i, (rand(8) + 2).to_s)
-      chars
+      session[:_rucaptcha] = RuCaptcha::Captcha.random_chars
+      RuCaptcha::Captcha.create(session[:_rucaptcha])
     end
 
     def verify_rucaptcha?(resource = nil)

lib/rucaptcha/version.rb

@@ -1,3 +1,3 @@
 module RuCaptcha
-  VERSION = '0.1.4'
+  VERSION = '0.2.0'
 end