diff --git a/api_docs/changelog.md b/api_docs/changelog.md
index dba6d76e08..7e4161582c 100644
--- a/api_docs/changelog.md
+++ b/api_docs/changelog.md
@@ -20,6 +20,12 @@ format used by the Zulip server that they are interacting with.
 
 ## Changes in Zulip 9.0
 
+**Feature level 276**
+
+* [Markdown message formatting](/api/message-formatting#image-previews):
+  Image preview elements not contain a `data-original-dimensions`
+  attribute containing the dimensions of the original image.
+
 **Feature level 275**
 
 * [`POST /register`](/api/register-queue), [`PATCH
diff --git a/version.py b/version.py
index cdc2fce7a0..6d8b2deaa4 100644
--- a/version.py
+++ b/version.py
@@ -34,7 +34,7 @@ DESKTOP_WARNING_VERSION = "5.9.3"
 # new level means in api_docs/changelog.md, as well as "**Changes**"
 # entries in the endpoint's documentation in `zulip.yaml`.
 
-API_FEATURE_LEVEL = 275  # Last bumped for `web_animate_image_previews` setting.
+API_FEATURE_LEVEL = 276  # Last bumped for data-original-dimensions
 
 
 # Bump the minor PROVISION_VERSION to indicate that folks should provision
diff --git a/zerver/lib/thumbnail.py b/zerver/lib/thumbnail.py
index 7718fc02bd..fd18392fe0 100644
--- a/zerver/lib/thumbnail.py
+++ b/zerver/lib/thumbnail.py
@@ -329,6 +329,8 @@ def split_thumbnail_path(file_path: str) -> tuple[str, BaseThumbnailFormat]:
 class MarkdownImageMetadata:
     url: str
     is_animated: bool
+    original_width_px: int
+    original_height_px: int
 
 
 def get_user_upload_previews(
@@ -347,6 +349,8 @@ def get_user_upload_previews(
             upload_preview_data[image_attachment.path_id] = MarkdownImageMetadata(
                 url=url,
                 is_animated=is_animated,
+                original_width_px=image_attachment.original_width_px,
+                original_height_px=image_attachment.original_height_px,
             )
     return upload_preview_data
 
@@ -421,6 +425,9 @@ def rewrite_thumbnailed_images(
             changed = True
             del image_tag["class"]
             image_tag["src"] = image_data.url
+            image_tag["data-original-dimensions"] = (
+                f"{image_data.original_width_px}x{image_data.original_height_px}"
+            )
             if image_data.is_animated:
                 image_tag["data-animated"] = "true"
 
diff --git a/zerver/tests/test_markdown_thumbnail.py b/zerver/tests/test_markdown_thumbnail.py
index b352b1c0eb..b68d4a3e21 100644
--- a/zerver/tests/test_markdown_thumbnail.py
+++ b/zerver/tests/test_markdown_thumbnail.py
@@ -73,15 +73,15 @@ class MarkdownThumbnailTest(ZulipTestCase):
                 "<p>Test 1<br>\n"
                 f'<a href="/user_uploads/{path_ids[0]}">{image_names[0]}</a> </p>\n'
                 f'<div class="message_inline_image"><a href="/user_uploads/{path_ids[0]}" title="{image_names[0]}">'
-                f'<img src="/user_uploads/thumbnail/{path_ids[0]}/840x560.webp"></a></div>'
+                f'<img data-original-dimensions="128x128" src="/user_uploads/thumbnail/{path_ids[0]}/840x560.webp"></a></div>'
                 "<p>Next image<br>\n"
                 f'<a href="/user_uploads/{path_ids[1]}">{image_names[1]}</a> </p>\n'
                 f'<div class="message_inline_image"><a href="/user_uploads/{path_ids[1]}" title="{image_names[1]}">'
-                f'<img src="/user_uploads/thumbnail/{path_ids[1]}/840x560.webp"></a></div>'
+                f'<img data-original-dimensions="128x128" src="/user_uploads/thumbnail/{path_ids[1]}/840x560.webp"></a></div>'
                 "<p>Another screenshot<br>\n"
                 f'<a href="/user_uploads/{path_ids[2]}">{image_names[2]}</a></p>\n'
                 f'<div class="message_inline_image"><a href="/user_uploads/{path_ids[2]}" title="{image_names[2]}">'
-                f'<img src="/user_uploads/thumbnail/{path_ids[2]}/840x560.webp"></a></div>'
+                f'<img data-original-dimensions="128x128" src="/user_uploads/thumbnail/{path_ids[2]}/840x560.webp"></a></div>'
             ),
         )
 
@@ -124,7 +124,7 @@ class MarkdownThumbnailTest(ZulipTestCase):
         expected = (
             f'<p><a href="/user_uploads/{path_id}">image</a></p>\n'
             f'<div class="message_inline_image"><a href="/user_uploads/{path_id}" title="image">'
-            f'<img src="/user_uploads/thumbnail/{path_id}/840x560.webp"></a></div>'
+            f'<img data-original-dimensions="128x128" src="/user_uploads/thumbnail/{path_id}/840x560.webp"></a></div>'
         )
         self.assert_message_content_is(message_id, expected)
 
@@ -142,7 +142,8 @@ class MarkdownThumbnailTest(ZulipTestCase):
         message_id = self.send_message_content(f"[I am 95% ± 5% certain!](/user_uploads/{path_id})")
         expected = (
             f'<p><a href="/user_uploads/{path_id}">I am 95% &plusmn; 5% certain!</a></p>\n'
-            f'<div class="message_inline_image"><a href="/user_uploads/{path_id}" title="I am 95% &plusmn; 5% certain!"><img src="/user_uploads/thumbnail/{path_id}/840x560.webp"></a></div>'
+            f'<div class="message_inline_image"><a href="/user_uploads/{path_id}" title="I am 95% &plusmn; 5% certain!">'
+            f'<img data-original-dimensions="128x128" src="/user_uploads/thumbnail/{path_id}/840x560.webp"></a></div>'
         )
         self.assert_message_content_is(message_id, expected)
 
@@ -157,12 +158,13 @@ class MarkdownThumbnailTest(ZulipTestCase):
             ThumbnailFormat("webp", 100, 75, animated=True),
             ThumbnailFormat("webp", 100, 75, animated=False),
         ):
-            path_id = self.upload_and_thumbnail_image("animated_img.gif")
-            content = f"[animated_img.gif](/user_uploads/{path_id})"
+            path_id = self.upload_and_thumbnail_image("animated_unequal_img.gif")
+            content = f"[animated_unequal_img.gif](/user_uploads/{path_id})"
             expected = (
-                f'<p><a href="/user_uploads/{path_id}">animated_img.gif</a></p>\n'
-                f'<div class="message_inline_image"><a href="/user_uploads/{path_id}" title="animated_img.gif">'
-                f'<img data-animated="true" src="/user_uploads/thumbnail/{path_id}/100x75-anim.webp"></a></div>'
+                f'<p><a href="/user_uploads/{path_id}">animated_unequal_img.gif</a></p>\n'
+                f'<div class="message_inline_image"><a href="/user_uploads/{path_id}" title="animated_unequal_img.gif">'
+                '<img data-animated="true" data-original-dimensions="128x56"'
+                f' src="/user_uploads/thumbnail/{path_id}/100x75-anim.webp"></a></div>'
             )
             message_id = self.send_message_content(content, do_thumbnail=True)
         self.assert_message_content_is(message_id, expected)
@@ -208,7 +210,7 @@ class MarkdownThumbnailTest(ZulipTestCase):
                 f'<div class="message_inline_image"><a href="/user_uploads/{first_path_id}" title="first image">'
                 '<img class="image-loading-placeholder" src="/static/images/loading/loader-black.svg"></a></div>'
                 f'<div class="message_inline_image"><a href="/user_uploads/{second_path_id}" title="second image">'
-                f'<img src="/user_uploads/thumbnail/{second_path_id}/840x560.webp"></a></div>'
+                f'<img data-original-dimensions="128x128" src="/user_uploads/thumbnail/{second_path_id}/840x560.webp"></a></div>'
             ),
         )
 
@@ -220,9 +222,9 @@ class MarkdownThumbnailTest(ZulipTestCase):
                 f'<p><a href="/user_uploads/{first_path_id}">first image</a><br>\n'
                 f'<a href="/user_uploads/{second_path_id}">second image</a></p>\n'
                 f'<div class="message_inline_image"><a href="/user_uploads/{first_path_id}" title="first image">'
-                f'<img src="/user_uploads/thumbnail/{first_path_id}/840x560.webp"></a></div>'
+                f'<img data-original-dimensions="128x128" src="/user_uploads/thumbnail/{first_path_id}/840x560.webp"></a></div>'
                 f'<div class="message_inline_image"><a href="/user_uploads/{second_path_id}" title="second image">'
-                f'<img src="/user_uploads/thumbnail/{second_path_id}/840x560.webp"></a></div>'
+                f'<img data-original-dimensions="128x128" src="/user_uploads/thumbnail/{second_path_id}/840x560.webp"></a></div>'
             ),
         )
 
@@ -247,7 +249,7 @@ class MarkdownThumbnailTest(ZulipTestCase):
         expected = (
             f'<p><a href="/user_uploads/{path_id}">image</a></p>\n'
             f'<div class="message_inline_image"><a href="/user_uploads/{path_id}" title="image">'
-            f'<img src="/user_uploads/thumbnail/{path_id}/840x560.webp"></a></div>'
+            f'<img data-original-dimensions="128x128" src="/user_uploads/thumbnail/{path_id}/840x560.webp"></a></div>'
         )
         self.assertEqual(
             ArchivedMessage.objects.get(id=message_id).rendered_content,
@@ -320,7 +322,7 @@ class MarkdownThumbnailTest(ZulipTestCase):
 
         rendered_thumb = (
             f'<div class="message_inline_image"><a href="/user_uploads/{path_id}" title="image">'
-            f'<img src="/user_uploads/thumbnail/{path_id}/100x75.webp"></a></div>'
+            f'<img data-original-dimensions="128x128" src="/user_uploads/thumbnail/{path_id}/100x75.webp"></a></div>'
         )
 
         self.assert_message_content_is(
diff --git a/zerver/worker/thumbnail.py b/zerver/worker/thumbnail.py
index aef0a50e7b..9e5854e06c 100644
--- a/zerver/worker/thumbnail.py
+++ b/zerver/worker/thumbnail.py
@@ -147,6 +147,8 @@ def ensure_thumbnails(image_attachment: ImageAttachment) -> int:
         MarkdownImageMetadata(
             url=url,
             is_animated=is_animated,
+            original_width_px=image_attachment.original_width_px,
+            original_height_px=image_attachment.original_height_px,
         ),
     )
     return written_images