diff --git a/.gitignore b/.gitignore
index ce0e20c..f80b5fd 100644
--- a/.gitignore
+++ b/.gitignore
@@ -7,7 +7,7 @@
 /spec/reports/
 /test/tmp/
 /test/version_tmp/
-!/tmp/
+/tmp/
 .DS_Store
 
 ## Specific to RubyMotion:
diff --git a/CHANGELOG.md b/CHANGELOG.md
index ce7d2fe..e531895 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,3 +1,10 @@
+0.2.0
+-----
+
+- Added file cache, can setup how many images you want generate by `config.cache_limit`,
+  RuCaptcha will use cache for next requests.
+  When you restart Rails processes it will generate new again and clean the old caches.
+
 0.1.4
 -----
 
diff --git a/Gemfile.lock b/Gemfile.lock
index 2300048..a210923 100644
--- a/Gemfile.lock
+++ b/Gemfile.lock
@@ -1,7 +1,7 @@
 PATH
   remote: .
   specs:
-    rucaptcha (0.1.4)
+    rucaptcha (0.2.0)
       posix-spawn (>= 0.3.0)
 
 GEM
diff --git a/README.md b/README.md
index 9f526cf..b8beebe 100644
--- a/README.md
+++ b/README.md
@@ -11,17 +11,37 @@ Idea by: https://ruby-china.org/topics/20558#reply4
 
 [中文介绍和使用说明](https://ruby-china.org/topics/27832)
 
-### Requirements
+
+## Feature
+
+- Only need `ImageMagick`, No `RMagick`, No `mini_magick`;
+- For Rails Application;
+- Simple, Easy to use;
+- File Caching for performance.
+
+## Requirements
 
 - ImageMagick
 
-### Example
+#### Ubuntu
+
+```
+sudo apt-get install imagemagick
+```
+
+#### Mac OS X
+
+```bash
+brew install imagemagick ghostscript
+```
+
+## Example
 
 ![rucaptcha1](https://cloud.githubusercontent.com/assets/5518/10726119/a844dfce-7c0b-11e5-99c3-a818f3ef3dd2.png) ![rucaptcha2](https://cloud.githubusercontent.com/assets/5518/10747608/2f2f5f10-7c92-11e5-860b-914db5695a57.png) ![rucaptcha3](https://cloud.githubusercontent.com/assets/5518/10747609/2f5bbac4-7c92-11e5-8192-4aa5dfb025b7.png) ![rucaptcha4](https://cloud.githubusercontent.com/assets/5518/10747611/2f7c6a12-7c92-11e5-8730-de7295b36dd6.png) ![rucaptcha5](https://cloud.githubusercontent.com/assets/5518/10747610/2f7a9d86-7c92-11e5-911a-44596c9aeef5.png)
 
 
 
-### Usage
+## Usage
 
 Put rucaptcha in your `Gemfile`:
 
@@ -39,6 +59,9 @@ RuCaptcha.configure do
   self.width = 180
   # Image height, default: 48
   self.height = 48
+  # Cache generated images in file store, this is config files limit, default: 100
+  # set 0 to disable file cache.
+  self.cache_limit = 100
 end
 ```
 
@@ -80,7 +103,7 @@ View `app/views/account/new.html.erb`
 </form>
 ```
 
-## Test skip captcha validation
+### Write your test skip captcha validation
 
 ```rb
 describe 'sign up and login', type: :feature do
@@ -92,7 +115,5 @@ describe 'sign up and login', type: :feature do
 end
 ```
 
-## TODO
 
-- Use [rtesseract](https://github.com/dannnylo/rtesseract) to test OCR.
 
diff --git a/lib/rucaptcha.rb b/lib/rucaptcha.rb
index a75661a..ccb0472 100644
--- a/lib/rucaptcha.rb
+++ b/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)
diff --git a/lib/rucaptcha/cache.rb b/lib/rucaptcha/cache.rb
new file mode 100644
index 0000000..783f7bd
--- /dev/null
+++ b/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
diff --git a/lib/rucaptcha/captcha.rb b/lib/rucaptcha/captcha.rb
index b5a6497..ea4790d 100644
--- a/lib/rucaptcha/captcha.rb
+++ b/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
diff --git a/lib/rucaptcha/configuration.rb b/lib/rucaptcha/configuration.rb
index 0ce026a..570ce97 100644
--- a/lib/rucaptcha/configuration.rb
+++ b/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
diff --git a/lib/rucaptcha/controller_helpers.rb b/lib/rucaptcha/controller_helpers.rb
index a5c68ca..ac669c2 100644
--- a/lib/rucaptcha/controller_helpers.rb
+++ b/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)
diff --git a/lib/rucaptcha/version.rb b/lib/rucaptcha/version.rb
index 515cd1c..4269518 100644
--- a/lib/rucaptcha/version.rb
+++ b/lib/rucaptcha/version.rb
@@ -1,3 +1,3 @@
 module RuCaptcha
-  VERSION = '0.1.4'
+  VERSION = '0.2.0'
 end
diff --git a/spec/cache_spec.rb b/spec/cache_spec.rb
new file mode 100644
index 0000000..4cab649
--- /dev/null
+++ b/spec/cache_spec.rb
@@ -0,0 +1,22 @@
+require 'spec_helper'
+
+describe RuCaptcha::Cache do
+  describe '.random_chars_with_cache' do
+    it 'should generate max chars by config.cache_limit' do
+      allow(RuCaptcha.config).to receive(:cache_limit).and_return(5)
+      items = []
+      10.times do
+        items << RuCaptcha::Captcha.random_chars_with_cache
+      end
+      expect(items.uniq.length).to eq 5
+      expect(RuCaptcha::Captcha.cached_codes).to eq items.uniq
+    end
+  end
+
+  describe '.create' do
+    it 'should work' do
+      expect(RuCaptcha::Captcha).to receive(:create_without_cache).and_return('aabb')
+      expect(RuCaptcha::Captcha.create('abcd')).to eq('aabb')
+    end
+  end
+end
diff --git a/spec/captcha_spec.rb b/spec/captcha_spec.rb
new file mode 100644
index 0000000..a67a9a4
--- /dev/null
+++ b/spec/captcha_spec.rb
@@ -0,0 +1,19 @@
+require 'spec_helper'
+
+describe RuCaptcha::Captcha do
+  describe '.random_chars' do
+    it 'should len equal config.len' do
+      expect(RuCaptcha::Captcha.random_chars_without_cache.length).to eq(RuCaptcha.config.len)
+    end
+
+    it 'should return 0-9 and lower str' do
+      expect(RuCaptcha::Captcha.random_chars_without_cache).to match(/[a-z0-9]/)
+    end
+
+    it 'should not include [0ol1]' do
+      10000.times do
+        expect(RuCaptcha::Captcha.random_chars_without_cache).not_to match(/[0ol1]/i)
+      end
+    end
+  end
+end
diff --git a/spec/controller_helpers_spec.rb b/spec/controller_helpers_spec.rb
index 1a3ecc1..77beec9 100644
--- a/spec/controller_helpers_spec.rb
+++ b/spec/controller_helpers_spec.rb
@@ -15,28 +15,12 @@ describe RuCaptcha do
 
   describe '.generate_rucaptcha' do
     it 'should work' do
-      expect(simple).to receive(:random_rucaptcha_chars).and_return('abcd')
+      expect(RuCaptcha::Captcha).to receive(:random_chars).and_return('abcd')
       expect(simple.generate_rucaptcha).not_to be_nil
       expect(simple.session[:_rucaptcha]).to eq('abcd')
     end
   end
 
-  describe '.random_rucaptcha_chars' do
-    it 'should len equal config.len' do
-      expect(simple.random_rucaptcha_chars.length).to eq(RuCaptcha.config.len)
-    end
-
-    it 'should return 0-9 and lower str' do
-      expect(simple.random_rucaptcha_chars).to match(/[a-z0-9]/)
-    end
-
-    it 'should not include [0ol1]' do
-      10000.times do
-        expect(simple.random_rucaptcha_chars).not_to match(/[0ol1]/i)
-      end
-    end
-  end
-
   describe '.verify_rucaptcha?' do
     context 'Correct chars in params' do
       it 'should work' do
diff --git a/spec/ocr_spec.rb b/spec/ocr_spec.rb
index 6942773..efe9e38 100644
--- a/spec/ocr_spec.rb
+++ b/spec/ocr_spec.rb
@@ -1,4 +1,5 @@
 require 'spec_helper'
+require 'fileutils'
 
 describe 'OCR' do
   before do
@@ -18,7 +19,8 @@ describe 'OCR' do
   end
 
   after do
-    `rm #{File.join(File.dirname(__FILE__), '../tmp/*.png')}`
+    path = File.expand_path File.join(File.dirname(__FILE__), '..', 'tmp/*.png')
+    FileUtils.rm_f(path)
   end
 
   it 'should not read by OCR lib' do
diff --git a/spec/spec_helper.rb b/spec/spec_helper.rb
index 8eaa0d4..86cb03b 100644
--- a/spec/spec_helper.rb
+++ b/spec/spec_helper.rb
@@ -11,6 +11,14 @@ if !File.exists?(tmp_path)
   Dir.mkdir(tmp_path)
 end
 
+module Rails
+  class << self
+    def root
+      Pathname.new(File.join(File.dirname(__FILE__), '..'))
+    end
+  end
+end
+
 RuCaptcha.configure do
   self.len = 2
   self.width = 123