diff --git a/lib/compass/configuration.rb b/lib/compass/configuration.rb
index 79b3b3f2..dc23077a 100644
--- a/lib/compass/configuration.rb
+++ b/lib/compass/configuration.rb
@@ -40,7 +40,8 @@ module Compass
       :preferred_syntax,
       :disable_warnings,
       :sprite_engine,
-      :chunky_png_options
+      :chunky_png_options,
+      :images_file_source
     ].flatten
 
     ARRAY_ATTRIBUTES = [
diff --git a/lib/compass/sass_extensions/functions/image_size.rb b/lib/compass/sass_extensions/functions/image_size.rb
index 97bf85c3..436c4de7 100644
--- a/lib/compass/sass_extensions/functions/image_size.rb
+++ b/lib/compass/sass_extensions/functions/image_size.rb
@@ -4,7 +4,7 @@ module Compass::SassExtensions::Functions::ImageSize
     width, _ = image_dimensions(image_file)
     Sass::Script::Number.new(width,["px"])
   end
-  
+
   # Returns the height of the image relative to the images directory
   def image_height(image_file)
     _, height = image_dimensions(image_file)
@@ -23,13 +23,23 @@ module Compass::SassExtensions::Functions::ImageSize
       raise Sass::SyntaxError, "Unrecognized file type: #{@file_type}"
     end
 
-  private
+    private
+    def open_file_source
+      source = Compass.configuration.images_file_source || lambda { |file| File.open(file, 'rb') }
+
+      io = source.call(@file)
+      result = yield io
+      io.close
+
+      result
+    end
+
     def get_size_for_png
-      File.open(@file, "rb") {|io| io.read}[0x10..0x18].unpack('NN')
+      open_file_source {|io| io.read}[0x10..0x18].unpack('NN')
     end
 
     def get_size_for_gif
-      File.open(@file, "rb") {|io| io.read}[6..10].unpack('SS')
+      open_file_source {|io| io.read}[6..10].unpack('SS')
     end
 
     def get_size_for_jpg
@@ -37,22 +47,24 @@ module Compass::SassExtensions::Functions::ImageSize
     end
 
     def get_size_for_jpeg
-      jpeg = JPEG.new(@file)
-      [jpeg.width, jpeg.height]
+      open_file_source do |io|
+        jpeg = JPEG.new(io)
+        [ jpeg.width, jpeg.height ]
+      end
     end
   end
 
-private
+  private
 
   def image_dimensions(image_file)
     options[:compass] ||= {}
     options[:compass][:image_dimensions] ||= {}
     options[:compass][:image_dimensions][image_file.value] = ImageProperties.new(image_path_for_size(image_file.value)).size
   end
-  
+
   def image_path_for_size(image_file)
     if File.exists?(image_file)
-      return image_file 
+      return image_file
     end
     real_path(image_file)
   end
@@ -69,15 +81,11 @@ private
   class JPEG
     attr_reader :width, :height, :bits
 
-    def initialize(file)
-      if file.kind_of? IO
-        examine(file)
-      else
-        File.open(file, 'rb') { |io| examine(io) }
-      end
+    def initialize(io)
+      examine(io)
     end
 
-  private
+    private
     def examine(io)
       class << io
         unless method_defined?(:readbyte)
@@ -99,15 +107,15 @@ private
 
       while marker = io.next
         case marker
-          when 0xC0..0xC3, 0xC5..0xC7, 0xC9..0xCB, 0xCD..0xCF # SOF markers
-            length, @bits, @height, @width, components = io.readsof
-            raise 'malformed JPEG' unless length == 8 + components * 3
-          when 0xD9, 0xDA then  break # EOI, SOS
-          when 0xFE then @comment = io.readframe # COM
-          when 0xE1 then io.readframe # APP1, contains EXIF tag
-          else io.readframe # ignore frame
+        when 0xC0..0xC3, 0xC5..0xC7, 0xC9..0xCB, 0xCD..0xCF # SOF markers
+          length, @bits, @height, @width, components = io.readsof
+          raise 'malformed JPEG' unless length == 8 + components * 3
+        when 0xD9, 0xDA then  break # EOI, SOS
+        when 0xFE then @comment = io.readframe # COM
+        when 0xE1 then io.readframe # APP1, contains EXIF tag
+        else io.readframe # ignore frame
         end
       end
     end
-end
+  end
 end
diff --git a/test/units/sass_extensions_test.rb b/test/units/sass_extensions_test.rb
index 67ffb895..bf989b3f 100644
--- a/test/units/sass_extensions_test.rb
+++ b/test/units/sass_extensions_test.rb
@@ -166,16 +166,29 @@ class SassExtensionsTest < Test::Unit::TestCase
     base64_string = File.read(File.join(Compass.configuration.fonts_path, "bgrove.base64.txt")).chomp
     assert_equal "url('data:font/truetype;base64,#{base64_string}') format('truetype')", evaluate("inline_font_files('bgrove.ttf', truetype)")
   end
-  
-  
+
   def test_image_size_should_respond_to_to_path
     object = mock()
     object.expects(:to_path).returns('foo.jpg')
     object.expects(:respond_to?).with(:to_path).returns(true)
-    
+
     Compass::SassExtensions::Functions::ImageSize::ImageProperties.new(object)
   end
-  
+
+  def test_image_properites_should_be_able_to_use_file_like_object
+    source = Class.new do
+      def self.open(*args, &block)
+        File.open(*args, &block)
+      end
+    end
+
+    Compass.configuration.images_file_source = lambda { |file| source.open(file) }
+
+    properties = Compass::SassExtensions::Functions::ImageSize::ImageProperties.new('test/fixtures/sprites/public/images/colors/blue.png')
+
+    assert_equal [ 10, 10 ], properties.size
+  end
+
   def test_reject
     assert_equal "b d", evaluate("reject(a b c d, a, c)")
     assert_equal "a b c d", evaluate("reject(a b c d, e)")