diff --git a/README.md b/README.md
index c7c6d2c..061d8c6 100644
--- a/README.md
+++ b/README.md
@@ -64,6 +64,13 @@ responsive_image:
   #   %{height}      Height of the resized image
   #
   output_path_format: assets/resized/%{width}/%{basename}
+
+  # By default, only images referenced by the responsive_image and responsive_image_block
+  # tags are resized. Here you can set a list of paths or path globs to resize other
+  # images. This is useful for resizing images which will be referenced from stylesheets.
+  extra_images:
+    - assets/foo/bar.png
+    - assets/bgs/*.png
 ```
 
 ## Usage
diff --git a/features/extra-image-generation.feature b/features/extra-image-generation.feature
new file mode 100644
index 0000000..49f9151
--- /dev/null
+++ b/features/extra-image-generation.feature
@@ -0,0 +1,43 @@
+Feature: Extra image generation
+  As a Jekyll user
+  I want to resize images that aren't used in posts or pages
+  In order to use them in my stylesheets
+
+  Scenario: Resizing a single image
+    Given I have a responsive_image configuration with:
+      """
+        sizes:
+          - width: 100
+
+        extra_images:
+          - assets/test.png
+      """
+
+    And I have a file "index.html" with "Hello, world!"
+    When I run Jekyll
+    Then the image "assets/resized/test-100x50.png" should have the dimensions "100x50"
+
+  Scenario: Using glob patterns
+    Given I have a responsive_image configuration with:
+      """
+        sizes:
+          - width: 100
+
+        extra_images:
+          - assets/*.png
+      """
+
+    And I have a file "index.html" with "Hello, world!"
+    When I run Jekyll
+    Then the image "assets/resized/test-100x50.png" should have the dimensions "100x50"
+
+  Scenario: No extra images
+    Given I have a responsive_image configuration with:
+      """
+        sizes:
+          - width: 100
+      """
+
+    And I have a file "index.html" with "Hello, world!"
+    When I run Jekyll
+    Then the file "assets/resized/test-100x50.png" should not exist
diff --git a/features/step_definitions/jekyll_steps.rb b/features/step_definitions/jekyll_steps.rb
index 0990a53..07899c9 100644
--- a/features/step_definitions/jekyll_steps.rb
+++ b/features/step_definitions/jekyll_steps.rb
@@ -33,7 +33,11 @@ Then /^I should see "(.+)" in "(.*)"$/ do |text, file|
 end
 
 Then /^the file "(.+)" should exist$/ do |path|
-  assert File.exists?(path)
+  assert File.exist?(path)
+end
+
+Then /^the file "(.+)" should not exist$/ do |path|
+  assert !File.exist?(path)
 end
 
 Then /^the image "(.+)" should have the dimensions "(\d+)x(\d+)"$/ do |path, width, height|
diff --git a/lib/jekyll/responsive_image.rb b/lib/jekyll/responsive_image.rb
index 06fd05c..70c3de9 100644
--- a/lib/jekyll/responsive_image.rb
+++ b/lib/jekyll/responsive_image.rb
@@ -13,6 +13,7 @@ require 'jekyll/responsive_image/resize_handler'
 require 'jekyll/responsive_image/common'
 require 'jekyll/responsive_image/tag'
 require 'jekyll/responsive_image/block'
+require 'jekyll/responsive_image/extra_image_generator'
 
 Liquid::Template.register_tag('responsive_image', Jekyll::ResponsiveImage::Tag)
 Liquid::Template.register_tag('responsive_image_block', Jekyll::ResponsiveImage::Block)
diff --git a/lib/jekyll/responsive_image/defaults.rb b/lib/jekyll/responsive_image/defaults.rb
index 6bd6532..c8ddc5f 100644
--- a/lib/jekyll/responsive_image/defaults.rb
+++ b/lib/jekyll/responsive_image/defaults.rb
@@ -5,6 +5,7 @@ module Jekyll
       'base_path'          => 'assets',
       'output_path_format' => 'assets/resized/%{filename}-%{width}x%{height}.%{extension}',
       'sizes'              => [],
+      'extra_images'       => []
     }.freeze
 
     class << self
diff --git a/lib/jekyll/responsive_image/extra_image_generator.rb b/lib/jekyll/responsive_image/extra_image_generator.rb
new file mode 100644
index 0000000..dc72f34
--- /dev/null
+++ b/lib/jekyll/responsive_image/extra_image_generator.rb
@@ -0,0 +1,15 @@
+module Jekyll
+  class ResponsiveImage
+    class ExtraImageGenerator < Jekyll::Generator
+      include Jekyll::ResponsiveImage::Common
+
+      def generate(site)
+        config = make_config(site)
+
+        config['extra_images'].each do |pathspec|
+          Dir.glob(pathspec) { |path| ImageProcessor.process(path, config) }
+        end
+      end
+    end
+  end
+end
diff --git a/lib/jekyll/responsive_image/image_processor.rb b/lib/jekyll/responsive_image/image_processor.rb
index 7e7632f..cbae275 100644
--- a/lib/jekyll/responsive_image/image_processor.rb
+++ b/lib/jekyll/responsive_image/image_processor.rb
@@ -4,7 +4,7 @@ module Jekyll
       include ResponsiveImage::Utils
 
       def process(image_path, config)
-        raise SyntaxError.new("Invalid image path specified: #{image_path}") unless File.exists?(image_path.to_s)
+        raise SyntaxError.new("Invalid image path specified: #{image_path}") unless File.exist?(image_path.to_s)
 
         resize_handler = ResizeHandler.new
         img = Magick::Image::read(image_path).first
diff --git a/lib/jekyll/responsive_image/resize_handler.rb b/lib/jekyll/responsive_image/resize_handler.rb
index b63c4db..6fbe8d6 100644
--- a/lib/jekyll/responsive_image/resize_handler.rb
+++ b/lib/jekyll/responsive_image/resize_handler.rb
@@ -17,7 +17,7 @@ module Jekyll
           resized.push(image_hash(config['base_path'], filepath, width, height))
 
           # Don't resize images more than once
-          next if File.exists?(filepath)
+          next if File.exist?(filepath)
 
           ensure_output_dir_exists!(File.dirname(filepath))
 
@@ -35,7 +35,7 @@ module Jekyll
 
           i.destroy!
         end
-        
+
         img.destroy!
 
         resized
@@ -46,7 +46,7 @@ module Jekyll
       end
 
       def ensure_output_dir_exists!(dir)
-        unless Dir.exists?(dir)
+        unless Dir.exist?(dir)
           Jekyll.logger.info "Creating output directory #{dir}"
           FileUtils.mkdir_p(dir)
         end