diff --git a/tools/releasetools/add_img_to_target_files.py b/tools/releasetools/add_img_to_target_files.py
index 70ea967..490b44a 100755
--- a/tools/releasetools/add_img_to_target_files.py
+++ b/tools/releasetools/add_img_to_target_files.py
@@ -60,6 +60,7 @@
 import common
 import rangelib
 import sparse_img
+import verity_utils
 
 if sys.hexversion < 0x02070000:
   print("Python 2.7 or newer is required.", file=sys.stderr)
@@ -312,6 +313,56 @@
   img.Write()
   return img.name
 
+def AddCustomImages(output_zip, partition_name):
+  """Adds and signs custom images in IMAGES/.
+
+  Args:
+    output_zip: The output zip file (needs to be already open), or None to
+        write images to OPTIONS.input_tmp/.
+
+  Uses the image under IMAGES/ if it already exists. Otherwise looks for the
+  image under PREBUILT_IMAGES/, signs it as needed, and returns the image name.
+
+  Raises:
+    AssertionError: If image can't be found.
+  """
+
+  partition_size = OPTIONS.info_dict.get(
+      "avb_{}_partition_size".format(partition_name))
+  key_path = OPTIONS.info_dict.get("avb_{}_key_path".format(partition_name))
+  algorithm = OPTIONS.info_dict.get("avb_{}_algorithm".format(partition_name))
+  extra_args = OPTIONS.info_dict.get(
+      "avb_{}_add_hashtree_footer_args".format(partition_name))
+  partition_size = OPTIONS.info_dict.get(
+      "avb_{}_partition_size".format(partition_name))
+
+  builder = verity_utils.CreateCustomImageBuilder(
+      OPTIONS.info_dict, partition_name, partition_size,
+      key_path, algorithm, extra_args)
+
+  for img_name in OPTIONS.info_dict.get(
+      "avb_{}_image_list".format(partition_name)).split():
+    custom_image = OutputFile(output_zip, OPTIONS.input_tmp, "IMAGES", img_name)
+    if os.path.exists(custom_image.name):
+      continue
+
+    custom_image_prebuilt_path = os.path.join(
+        OPTIONS.input_tmp, "PREBUILT_IMAGES", img_name)
+    assert os.path.exists(custom_image_prebuilt_path), \
+      "Failed to find %s at %s" % (img_name, custom_image_prebuilt_path)
+
+    shutil.copy(custom_image_prebuilt_path, custom_image.name)
+
+    if builder is not None:
+      builder.Build(custom_image.name)
+
+    custom_image.Write()
+
+  default = os.path.join(OPTIONS.input_tmp, "IMAGES", partition_name + ".img")
+  assert os.path.exists(default), \
+      "There should be one %s.img" % (partition_name)
+  return default
+
 
 def CreateImage(input_dir, info_dict, what, output_file, block_list=None):
   logger.info("creating %s.img...", what)
@@ -411,8 +462,9 @@
   Args:
     output_zip: The output zip file, which needs to be already open.
     partitions: A dict that's keyed by partition names with image paths as
-        values. Only valid partition names are accepted, as listed in
-        common.AVB_PARTITIONS.
+        values. Only valid partition names are accepted, as partitions listed
+        in common.AVB_PARTITIONS and custom partitions listed in
+        OPTIONS.info_dict.get("avb_custom_images_partition_list")
     name: Name of the VBMeta partition, e.g. 'vbmeta', 'vbmeta_system'.
     needed_partitions: Partitions whose descriptors should be included into the
         generated VBMeta image.
@@ -831,11 +883,20 @@
     banner("dtbo")
     partitions['dtbo'] = AddDtbo(output_zip)
 
+  # Custom images.
+  custom_partitions = OPTIONS.info_dict.get(
+      "avb_custom_images_partition_list", "").strip().split()
+  for partition_name in custom_partitions:
+    partition_name = partition_name.strip()
+    banner("custom images for " + partition_name)
+    partitions[partition_name] = AddCustomImages(output_zip, partition_name)
+
   if OPTIONS.info_dict.get("avb_enable") == "true":
     # vbmeta_partitions includes the partitions that should be included into
     # top-level vbmeta.img, which are the ones that are not included in any
     # chained VBMeta image plus the chained VBMeta images themselves.
-    vbmeta_partitions = common.AVB_PARTITIONS[:]
+    # Currently custom_partitions are all chained to VBMeta image.
+    vbmeta_partitions = common.AVB_PARTITIONS[:] + tuple(custom_partitions)
 
     vbmeta_system = OPTIONS.info_dict.get("avb_vbmeta_system", "").strip()
     if vbmeta_system:
diff --git a/tools/releasetools/common.py b/tools/releasetools/common.py
index 96f93a8..93e14e5 100644
--- a/tools/releasetools/common.py
+++ b/tools/releasetools/common.py
@@ -1132,8 +1132,9 @@
   Args:
     image_path: The output path for the new VBMeta image.
     partitions: A dict that's keyed by partition names with image paths as
-        values. Only valid partition names are accepted, as listed in
-        common.AVB_PARTITIONS.
+        values. Only valid partition names are accepted, as partitions listed
+        in common.AVB_PARTITIONS and custom partitions listed in
+        OPTIONS.info_dict.get("avb_custom_images_partition_list")
     name: Name of the VBMeta partition, e.g. 'vbmeta', 'vbmeta_system'.
     needed_partitions: Partitions whose descriptors should be included into the
         generated VBMeta image.
@@ -1145,11 +1146,15 @@
   cmd = [avbtool, "make_vbmeta_image", "--output", image_path]
   AppendAVBSigningArgs(cmd, name)
 
+  custom_partitions = OPTIONS.info_dict.get(
+      "avb_custom_images_partition_list", "").strip().split()
+
   for partition, path in partitions.items():
     if partition not in needed_partitions:
       continue
     assert (partition in AVB_PARTITIONS or
-            partition in AVB_VBMETA_PARTITIONS), \
+            partition in AVB_VBMETA_PARTITIONS or
+            partition in custom_partitions), \
         'Unknown partition: {}'.format(partition)
     assert os.path.exists(path), \
         'Failed to find {} for {}'.format(path, partition)
diff --git a/tools/releasetools/sign_target_files_apks.py b/tools/releasetools/sign_target_files_apks.py
index 52cd9a8..52b7889 100755
--- a/tools/releasetools/sign_target_files_apks.py
+++ b/tools/releasetools/sign_target_files_apks.py
@@ -112,6 +112,17 @@
       (e.g. "--signing_helper /path/to/helper"). The args will be appended to
       the existing ones in info dict.
 
+  --avb_extra_custom_image_key <partition=key>
+  --avb_extra_custom_image_algorithm <partition=algorithm>
+      Use the specified algorithm (e.g. SHA256_RSA4096) and the key to AVB-sign
+      the specified custom images mounted on the partition. Otherwise it uses
+      the existing values in info dict.
+
+  --avb_extra_custom_image_extra_args <partition=extra_args>
+      Specify any additional args that are needed to AVB-sign the custom images
+      mounted on the partition (e.g. "--signing_helper /path/to/helper"). The
+      args will be appended to the existing ones in info dict.
+
   --android_jar_path <path>
       Path to the android.jar to repack the apex file.
 """
@@ -956,12 +967,20 @@
     if extra_args:
       print('Setting extra AVB signing args for %s to "%s"' % (
           partition, extra_args))
-      args_key = AVB_FOOTER_ARGS_BY_PARTITION[partition]
+      if partition in AVB_FOOTER_ARGS_BY_PARTITION:
+        args_key = AVB_FOOTER_ARGS_BY_PARTITION[partition]
+      else:
+        # custom partition
+        args_key = "avb_{}_add_hashtree_footer_args".format(partition)
       misc_info[args_key] = (misc_info.get(args_key, '') + ' ' + extra_args)
 
   for partition in AVB_FOOTER_ARGS_BY_PARTITION:
     ReplaceAvbPartitionSigningKey(partition)
 
+  for custom_partition in misc_info.get(
+      "avb_custom_images_partition_list", "").strip().split():
+    ReplaceAvbPartitionSigningKey(custom_partition)
+
 
 def RewriteAvbProps(misc_info):
   """Rewrites the props in AVB signing args."""
@@ -1208,6 +1227,15 @@
       OPTIONS.avb_extra_args['vbmeta_vendor'] = a
     elif o == "--avb_apex_extra_args":
       OPTIONS.avb_extra_args['apex'] = a
+    elif o == "--avb_extra_custom_image_key":
+      partition, key = a.split("=")
+      OPTIONS.avb_keys[partition] = key
+    elif o == "--avb_extra_custom_image_algorithm":
+      partition, algorithm = a.split("=")
+      OPTIONS.avb_algorithms[partition] = algorithm
+    elif o == "--avb_extra_custom_image_extra_args":
+      partition, extra_args = a.split("=")
+      OPTIONS.avb_extra_args[partition] = extra_args
     else:
       return False
     return True
@@ -1252,6 +1280,9 @@
           "avb_vbmeta_vendor_algorithm=",
           "avb_vbmeta_vendor_key=",
           "avb_vbmeta_vendor_extra_args=",
+          "avb_extra_custom_image_key=",
+          "avb_extra_custom_image_algorithm=",
+          "avb_extra_custom_image_extra_args=",
       ],
       extra_option_handler=option_handler)
 
diff --git a/tools/releasetools/validate_target_files.py b/tools/releasetools/validate_target_files.py
index 1b918cc..69be511 100755
--- a/tools/releasetools/validate_target_files.py
+++ b/tools/releasetools/validate_target_files.py
@@ -352,8 +352,13 @@
     cmd = [info_dict['avb_avbtool'], 'verify_image', '--image', image,
            '--follow_chain_partitions']
 
+    # Custom images.
+    custom_partitions = info_dict.get(
+        "avb_custom_images_partition_list", "").strip().split()
+
     # Append the args for chained partitions if any.
-    for partition in common.AVB_PARTITIONS + common.AVB_VBMETA_PARTITIONS:
+    for partition in (common.AVB_PARTITIONS + common.AVB_VBMETA_PARTITIONS +
+                      tuple(custom_partitions)):
       key_name = 'avb_' + partition + '_key_path'
       if info_dict.get(key_name) is not None:
         if info_dict.get('ab_update') != 'true' and partition == 'recovery':
diff --git a/tools/releasetools/verity_utils.py b/tools/releasetools/verity_utils.py
index e7f84f5..fc83689 100644
--- a/tools/releasetools/verity_utils.py
+++ b/tools/releasetools/verity_utils.py
@@ -695,3 +695,22 @@
       raise HashtreeInfoGenerationError("Failed to reconstruct the verity tree")
 
     return self.hashtree_info
+
+
+def CreateCustomImageBuilder(info_dict, partition_name, partition_size,
+                            key_path, algorithm, signing_args):
+  builder = None
+  if info_dict.get("avb_enable") == "true":
+    builder = VerifiedBootVersion2VerityImageBuilder(
+        partition_name,
+        partition_size,
+        VerifiedBootVersion2VerityImageBuilder.AVB_HASHTREE_FOOTER,
+        info_dict.get("avb_avbtool"),
+        key_path,
+        algorithm,
+        # Salt is None because custom images have no fingerprint property to be
+        # used as the salt.
+        None,
+        signing_args)
+
+  return builder