diff --git a/tools/releasetools/common.py b/tools/releasetools/common.py
index 171c794..3e2a113 100644
--- a/tools/releasetools/common.py
+++ b/tools/releasetools/common.py
@@ -824,6 +824,77 @@
   return tmp
 
 
+def GetUserImage(which, tmpdir, input_zip,
+                 info_dict=None,
+                 allow_shared_blocks=None,
+                 hashtree_info_generator=None,
+                 reset_file_map=False):
+  """Returns an Image object suitable for passing to BlockImageDiff.
+
+  This function loads the specified image from the given path. If the specified
+  image is sparse, it also performs additional processing for OTA purpose. For
+  example, it always adds block 0 to clobbered blocks list. It also detects
+  files that cannot be reconstructed from the block list, for whom we should
+  avoid applying imgdiff.
+
+  Args:
+    which: The partition name.
+    tmpdir: The directory that contains the prebuilt image and block map file.
+    input_zip: The target-files ZIP archive.
+    info_dict: The dict to be looked up for relevant info.
+    allow_shared_blocks: If image is sparse, whether having shared blocks is
+        allowed. If none, it is looked up from info_dict.
+    hashtree_info_generator: If present and image is sparse, generates the
+        hashtree_info for this sparse image.
+    reset_file_map: If true and image is sparse, reset file map before returning
+        the image.
+  Returns:
+    A Image object. If it is a sparse image and reset_file_map is False, the
+    image will have file_map info loaded.
+  """
+  if info_dict == None:
+    info_dict = LoadInfoDict(input_zip)
+
+  is_sparse = info_dict.get("extfs_sparse_flag")
+
+  # When target uses 'BOARD_EXT4_SHARE_DUP_BLOCKS := true', images may contain
+  # shared blocks (i.e. some blocks will show up in multiple files' block
+  # list). We can only allocate such shared blocks to the first "owner", and
+  # disable imgdiff for all later occurrences.
+  if allow_shared_blocks is None:
+    allow_shared_blocks = info_dict.get("ext4_share_dup_blocks") == "true"
+
+  if is_sparse:
+    img = GetSparseImage(which, tmpdir, input_zip, allow_shared_blocks,
+                         hashtree_info_generator)
+    if reset_file_map:
+      img.ResetFileMap()
+    return img
+  else:
+    return GetNonSparseImage(which, tmpdir, hashtree_info_generator)
+
+
+def GetNonSparseImage(which, tmpdir, hashtree_info_generator=None):
+  """Returns a Image object suitable for passing to BlockImageDiff.
+
+  This function loads the specified non-sparse image from the given path.
+
+  Args:
+    which: The partition name.
+    tmpdir: The directory that contains the prebuilt image and block map file.
+  Returns:
+    A Image object.
+  """
+  path = os.path.join(tmpdir, "IMAGES", which + ".img")
+  mappath = os.path.join(tmpdir, "IMAGES", which + ".map")
+
+  # The image and map files must have been created prior to calling
+  # ota_from_target_files.py (since LMP).
+  assert os.path.exists(path) and os.path.exists(mappath)
+
+  return blockimgdiff.FileImage(path, hashtree_info_generator=
+                                hashtree_info_generator)
+
 def GetSparseImage(which, tmpdir, input_zip, allow_shared_blocks,
                    hashtree_info_generator=None):
   """Returns a SparseImage object suitable for passing to BlockImageDiff.
@@ -2068,7 +2139,7 @@
 
 
 DataImage = blockimgdiff.DataImage
-
+EmptyImage = blockimgdiff.EmptyImage
 
 # map recovery.fstab's fs_types to mount/format "partition types"
 PARTITION_TYPES = {