diff --git a/CHANGELOG.md b/CHANGELOG.md
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,16 +1,31 @@
 # Change log
 
-Release 0.1.1
+## Release 0.4.1
 
+* Added some regression tests
+* Simplified type architecture (no surface changes)
+
+## Release 0.4
+
+* Fixed an issue from version 0.3.1 where some type instances were missing to write images to disk.
+
+## Release 0.3.1
+
+* Change underlying image type to carry image format around.
+
+## Release 0.3
+
+* Refactored the internal structure to allow for composition of compilers
+
+## Release 0.1.1
+
 * Exposed `resizeImageCompiler` and `scaleImageCompiler` to the base `Hakyll.Images` module
 
-Release 0.1.0
--------------
+## Release 0.1.0
 
 * added `resizeImageCompiler` to resize images to a specific shape;
 * added `scaleImageCompiler` to scale images while keeping aspect ratio.
 
-Release 0.0.1
--------------
+## Release 0.0.1
 
 * Added compressJpgCompiler to compress JPEGs.
diff --git a/hakyll-images.cabal b/hakyll-images.cabal
--- a/hakyll-images.cabal
+++ b/hakyll-images.cabal
@@ -4,10 +4,10 @@
 --
 -- see: https://github.com/sol/hpack
 --
--- hash: 937597bab3f482f7bbc2688e6a13a148528dc5fbd319eceea97fd955b04b54fa
+-- hash: 8668d79c72dd31f545171175bf9caadb045ee31f00b196459adfa05a3c45a1b8
 
 name:           hakyll-images
-version:        0.4.0
+version:        0.4.1
 synopsis:       Hakyll utilities to work with images
 description:    hakyll-images is an add-on to the hakyll package. It adds utilities to work with images, including JPEG compression.
 category:       Web
diff --git a/library/Hakyll/Images/Common.hs b/library/Hakyll/Images/Common.hs
--- a/library/Hakyll/Images/Common.hs
+++ b/library/Hakyll/Images/Common.hs
@@ -12,11 +12,8 @@
 Portability : portable
 -}
 
-module Hakyll.Images.Common ( Image
-                            , Image_(..)
+module Hakyll.Images.Common ( Image(..)
                             , ImageFormat(..)
-                            , format
-                            , image
                             , loadImage
                             , encode
                             ) where
@@ -44,35 +41,26 @@
     | Tiff
     deriving (Eq, Generic)
 
+-- Automatic derivation of Binary instances requires Generic
 instance Binary ImageFormat
 
 -- Polymorphic type only to get an instance of functor.
 -- Do not use this type.
-data Image_ a = Image ImageFormat a 
+data Image = Image { format :: ImageFormat
+                   , image :: ByteString
+                   }
     deriving (Typeable)
 
-instance Functor Image_ where
-    fmap f (Image fmt a) = Image fmt (f a)
-
-type Image = Image_ ByteString
-
 -- When writing to disk, we ignore the image format.
 -- Trusting users to route correctly.
 instance Writable Image where
     -- Write the bytestring content
     write fp item  = write fp (image <$> item)
 
+-- Binary instance looks similar to the binary instance for a Hakyll Item
 instance Binary Image where
     put (Image fmt content) = put fmt >> put content
     get                     = Image <$> get <*> get
-
--- | Extract format from an image
-format :: Image_ a -> ImageFormat
-format (Image fmt _) = fmt
-
--- | Extract data from image
-image :: Image_ a -> a
-image (Image _ im) = im
 
 -- | Load an image from a file.
 -- This function can be combined with other compilers.
diff --git a/library/Hakyll/Images/CompressJpg.hs b/library/Hakyll/Images/CompressJpg.hs
--- a/library/Hakyll/Images/CompressJpg.hs
+++ b/library/Hakyll/Images/CompressJpg.hs
@@ -45,8 +45,7 @@
 import Hakyll.Core.Item                 (Item(..))
 import Hakyll.Core.Compiler             (Compiler)
 
-import Hakyll.Images.Common             ( Image
-                                        , Image_(..)
+import Hakyll.Images.Common             ( Image(..)
                                         , ImageFormat(..)
                                         , image
                                         , format
diff --git a/library/Hakyll/Images/Resize.hs b/library/Hakyll/Images/Resize.hs
--- a/library/Hakyll/Images/Resize.hs
+++ b/library/Hakyll/Images/Resize.hs
@@ -56,7 +56,7 @@
 import Hakyll.Core.Item         (Item(..))
 import Hakyll.Core.Compiler     (Compiler)
 
-import Hakyll.Images.Common     (Image, encode, format, image)
+import Hakyll.Images.Common     (Image(..), encode)
 
 type Width = Int
 type Height = Int
@@ -83,14 +83,16 @@
 --     compile $ loadImage 
 --         >>= resizeImageCompiler 48 64
 -- @
+--
+-- Note that in the resizing process, images will be converted to RGBA8.
 resizeImageCompiler :: Width -> Height -> Item Image -> Compiler (Item Image)
-resizeImageCompiler w h item = do
+resizeImageCompiler w h item =
     let fmt = (format . itemBody) item
-    return $ (encode fmt . resize w h . decodeImage' . image) <$> item
+    in return $ (encode fmt . resize w h . decodeImage' . image) <$> item
 
 -- | Scale an image to a size that will fit in the specified width and height,
 -- while preserving aspect ratio.
---
+-- 
 -- In the process, an image is converted to RGBA8. Therefore, some information
 -- loss may occur.
 scale :: Width -> Height -> DynamicImage -> DynamicImage
@@ -113,7 +115,9 @@
 --     compile $ loadImage 
 --         >>= scaleImageCompiler 48 64
 -- @
+--
+-- Note that in the resizing process, images will be converted to RGBA8.
 scaleImageCompiler :: Width -> Height -> Item Image -> Compiler (Item Image)
-scaleImageCompiler w h item = do
+scaleImageCompiler w h item =
     let fmt = (format . itemBody) item
-    return $ (encode fmt . scale w h . decodeImage' . image) <$> item
+    in return $ (encode fmt . scale w h . decodeImage' . image) <$> item
diff --git a/package.yaml b/package.yaml
--- a/package.yaml
+++ b/package.yaml
@@ -1,5 +1,5 @@
 name: hakyll-images
-version: '0.4.0'
+version: '0.4.1'
 github: "LaurentRDC/hakyll-images"
 license: BSD3
 author: "Laurent P. René de Cotret"
diff --git a/stack.yaml b/stack.yaml
--- a/stack.yaml
+++ b/stack.yaml
@@ -1,65 +1,65 @@
-# This file was automatically generated by 'stack init'
-#
-# Some commonly used options have been documented as comments in this file.
-# For advanced use and comprehensive documentation of the format, please see:
-# https://docs.haskellstack.org/en/stable/yaml_configuration/
-
-# Resolver to choose a 'specific' stackage snapshot or a compiler version.
-# A snapshot resolver dictates the compiler version and the set of packages
-# to be used for project dependencies. For example:
-#
-# resolver: lts-3.5
-# resolver: nightly-2015-09-21
-# resolver: ghc-7.10.2
-# resolver: ghcjs-0.1.0_ghc-7.10.2
-#
-# The location of a snapshot can be provided as a file or url. Stack assumes
-# a snapshot provided as a file might change, whereas a url resource does not.
-#
-# resolver: ./custom-snapshot.yaml
-# resolver: https://example.com/snapshots/2018-01-01.yaml
-resolver: lts-12.26
-
-# User packages to be built.
-# Various formats can be used as shown in the example below.
-#
-# packages:
-# - some-directory
-# - https://example.com/foo/bar/baz-0.0.2.tar.gz
-# - location:
-#    git: https://github.com/commercialhaskell/stack.git
-#    commit: e7b331f14bcffb8367cd58fbfc8b40ec7642100a
-# - location: https://github.com/commercialhaskell/stack/commit/e7b331f14bcffb8367cd58fbfc8b40ec7642100a
-#  subdirs:
-#  - auto-update
-#  - wai
-packages:
-- .
-# Dependency packages to be pulled from upstream that are not in the resolver
-# using the same syntax as the packages field.
-# (e.g., acme-missiles-0.3)
-# extra-deps: []
-
-# Override default flag values for local packages and extra-deps
-# flags: {}
-
-# Extra package databases containing global packages
-# extra-package-dbs: []
-
-# Control whether we use the GHC we find on the path
-# system-ghc: true
-#
-# Require a specific version of stack, using version ranges
-# require-stack-version: -any # Default
-# require-stack-version: ">=1.7"
-#
-# Override the architecture used by stack, especially useful on Windows
-# arch: i386
-# arch: x86_64
-#
-# Extra directories used by stack for building
-# extra-include-dirs: [/path/to/dir]
-# extra-lib-dirs: [/path/to/dir]
-#
-# Allow a newer minor version of GHC than the snapshot specifies
+# This file was automatically generated by 'stack init'
+#
+# Some commonly used options have been documented as comments in this file.
+# For advanced use and comprehensive documentation of the format, please see:
+# https://docs.haskellstack.org/en/stable/yaml_configuration/
+
+# Resolver to choose a 'specific' stackage snapshot or a compiler version.
+# A snapshot resolver dictates the compiler version and the set of packages
+# to be used for project dependencies. For example:
+#
+# resolver: lts-3.5
+# resolver: nightly-2015-09-21
+# resolver: ghc-7.10.2
+# resolver: ghcjs-0.1.0_ghc-7.10.2
+#
+# The location of a snapshot can be provided as a file or url. Stack assumes
+# a snapshot provided as a file might change, whereas a url resource does not.
+#
+# resolver: ./custom-snapshot.yaml
+# resolver: https://example.com/snapshots/2018-01-01.yaml
+resolver: lts-12.26
+
+# User packages to be built.
+# Various formats can be used as shown in the example below.
+#
+# packages:
+# - some-directory
+# - https://example.com/foo/bar/baz-0.0.2.tar.gz
+# - location:
+#    git: https://github.com/commercialhaskell/stack.git
+#    commit: e7b331f14bcffb8367cd58fbfc8b40ec7642100a
+# - location: https://github.com/commercialhaskell/stack/commit/e7b331f14bcffb8367cd58fbfc8b40ec7642100a
+#  subdirs:
+#  - auto-update
+#  - wai
+packages:
+- .
+# Dependency packages to be pulled from upstream that are not in the resolver
+# using the same syntax as the packages field.
+# (e.g., acme-missiles-0.3)
+# extra-deps: []
+
+# Override default flag values for local packages and extra-deps
+# flags: {}
+
+# Extra package databases containing global packages
+# extra-package-dbs: []
+
+# Control whether we use the GHC we find on the path
+# system-ghc: true
+#
+# Require a specific version of stack, using version ranges
+# require-stack-version: -any # Default
+# require-stack-version: ">=1.7"
+#
+# Override the architecture used by stack, especially useful on Windows
+# arch: i386
+# arch: x86_64
+#
+# Extra directories used by stack for building
+# extra-include-dirs: [/path/to/dir]
+# extra-lib-dirs: [/path/to/dir]
+#
+# Allow a newer minor version of GHC than the snapshot specifies
 # compiler-check: newer-minor