diff --git a/core/nwb.image.yaml b/core/nwb.image.yaml
index 11c36fb..3f782a6 100644
--- a/core/nwb.image.yaml
+++ b/core/nwb.image.yaml
@@ -118,7 +118,7 @@ groups:
 
 - neurodata_type_def: ImageMaskSeries
   neurodata_type_inc: ImageSeries
-  doc: An alpha mask that is applied to a presented visual stimulus. The 'data' array
+  doc: DEPRECATED. An alpha mask that is applied to a presented visual stimulus. The 'data' array
     contains an array of mask values that are applied to the displayed image. Mask
     values are stored as RGBA. Mask can vary with time. The timestamps array indicates
     the starting time of a mask, and that mask pattern continues until it's explicitly
diff --git a/docs/format/source/format_release_notes.rst b/docs/format/source/format_release_notes.rst
index 74225e4..a0f3efd 100644
--- a/docs/format/source/format_release_notes.rst
+++ b/docs/format/source/format_release_notes.rst
@@ -5,6 +5,7 @@ Release Notes
 
 2.8.0 (Upcoming)
 ------------------------
+
 Minor changes
 ^^^^^^^^^^^^^
 - Added support to set boundary metadata for ``SpatialSeries``. (#524)
@@ -14,6 +15,8 @@ Minor changes
   electrode and unit. (#576)
 - Added optional ``was_generated_by`` attribute to ``NWBFile`` to store provenance information (#578)
 
+- Deprecated ``ImageMaskSeries`` neurodata type. (#583)
+
 2.7.0 (February 7, 2024)
 ------------------------