diff --git a/docs/administration/management-commands.md b/docs/administration/management-commands.md
new file mode 100644
index 000000000..8fe0f0a26
--- /dev/null
+++ b/docs/administration/management-commands.md
@@ -0,0 +1,102 @@
+# Management Commands
+
+In addition to Django's built-in management commands, NetBox provides several commands of its own. These are run using `manage.py`:
+
+```
+cd /opt/netbox
+source /opt/netbox/venv/bin/activate
+python3 netbox/manage.py <command>
+```
+
+Run any command with `--help` to see its full set of arguments.
+
+## calculate_cached_counts
+
+Force a recalculation of all cached counter fields (for example, the device count shown on a site). NetBox keeps these counters current automatically; this command is useful to repair them if they have drifted.
+
+```
+python3 netbox/manage.py calculate_cached_counts
+```
+
+## nbshell
+
+Start the Django shell with all NetBox models already imported. See [NetBox Shell](./netbox-shell.md) for details.
+
+```
+python3 netbox/manage.py nbshell
+```
+
+## populate_image_sizes
+
+!!! info "This command was introduced in NetBox v4.6.4."
+
+Populate the cached file size for image attachments that predate the `image_size` field. Running this once after upgrading is recommended for deployments with many existing attachments on a remote storage backend (such as S3). It is safe to run on a live system and may be re-run; any file that cannot be read is skipped and retried on the next run.
+
+```
+python3 netbox/manage.py populate_image_sizes
+```
+
+## rebuild_prefixes
+
+Rebuild the IPAM prefix hierarchy, recalculating the depth and child counts for all prefixes.
+
+```
+python3 netbox/manage.py rebuild_prefixes
+```
+
+## reindex
+
+Reindex objects for the search backend. Pass one or more apps or models to reindex a subset; with no arguments, all models are reindexed. See [Removing a Plugin](../plugins/removal.md) for a related use.
+
+```
+python3 netbox/manage.py reindex [app_label[.ModelName] ...]
+```
+
+## renaturalize
+
+Recalculate natural ordering values for the affected models. Pass one or more `app_label.ModelName` arguments to limit the scope; with no arguments, all models with natural ordering fields are processed.
+
+```
+python3 netbox/manage.py renaturalize [app_label.ModelName ...]
+```
+
+## runscript
+
+Run a [custom script](../customization/custom-scripts.md) from the command line, outside the web UI or API.
+
+```
+python3 netbox/manage.py runscript <module.ScriptName>
+```
+
+## rqworker
+
+Start a background task worker to process queued jobs (provided by django-rq). At least one worker must be running for background tasks such as report and script execution, webhooks, and synchronization to be processed.
+
+```
+python3 netbox/manage.py rqworker
+```
+
+## syncdatasource
+
+Synchronize a data source from its remote upstream. Pass one or more data source names, or `--all` to synchronize every data source.
+
+```
+python3 netbox/manage.py syncdatasource <name> [<name> ...]
+python3 netbox/manage.py syncdatasource --all
+```
+
+## trace_paths
+
+Generate any missing cable paths among all cable termination objects. This is useful after a bulk import of cabling, or to repair paths that were not generated automatically.
+
+```
+python3 netbox/manage.py trace_paths
+```
+
+## webhook_receiver
+
+Start a simple HTTP listener that prints any requests it receives. This is a debugging aid for testing webhooks: point a webhook at the listener and inspect exactly what NetBox sends. It listens on port 9000 by default; pass `--port` to change it and `--no-headers` to suppress the request headers.
+
+```
+python3 netbox/manage.py webhook_receiver [--port PORT] [--no-headers]
+```
diff --git a/mkdocs.yml b/mkdocs.yml
index 637c02741..15a8fac81 100644
--- a/mkdocs.yml
+++ b/mkdocs.yml
@@ -170,6 +170,7 @@ nav:
             - Okta: 'administration/authentication/okta.md'
         - Permissions: 'administration/permissions.md'
         - Error Reporting: 'administration/error-reporting.md'
+        - Management Commands: 'administration/management-commands.md'
         - Replicating NetBox: 'administration/replicating-netbox.md'
         - NetBox Shell: 'administration/netbox-shell.md'
     - Data Model:
diff --git a/netbox/extras/api/serializers_/attachments.py b/netbox/extras/api/serializers_/attachments.py
index 613825203..07a709ecd 100644
--- a/netbox/extras/api/serializers_/attachments.py
+++ b/netbox/extras/api/serializers_/attachments.py
@@ -19,12 +19,13 @@ class ImageAttachmentSerializer(ValidatedModelSerializer):
     parent = GFKSerializerField(read_only=True)
     image_width = serializers.IntegerField(read_only=True)
     image_height = serializers.IntegerField(read_only=True)
+    image_size = serializers.IntegerField(read_only=True)
 
     class Meta:
         model = ImageAttachment
         fields = [
             'id', 'url', 'display', 'object_type', 'object_id', 'parent', 'name', 'image', 'description',
-            'image_height', 'image_width', 'created', 'last_updated',
+            'image_height', 'image_width', 'image_size', 'created', 'last_updated',
         ]
         brief_fields = ('id', 'url', 'display', 'name', 'image', 'description')
 
diff --git a/netbox/extras/filtersets.py b/netbox/extras/filtersets.py
index 8e9683636..8bb91ed0e 100644
--- a/netbox/extras/filtersets.py
+++ b/netbox/extras/filtersets.py
@@ -506,7 +506,9 @@ class ImageAttachmentFilterSet(ChangeLoggedModelFilterSet):
 
     class Meta:
         model = ImageAttachment
-        fields = ('id', 'object_type_id', 'object_id', 'name', 'description', 'image_width', 'image_height')
+        fields = (
+            'id', 'object_type_id', 'object_id', 'name', 'description', 'image_width', 'image_height', 'image_size',
+        )
 
     def search(self, queryset, name, value):
         if not value.strip():
diff --git a/netbox/extras/graphql/filters.py b/netbox/extras/graphql/filters.py
index 5b6e2eab6..271b209e2 100644
--- a/netbox/extras/graphql/filters.py
+++ b/netbox/extras/graphql/filters.py
@@ -24,7 +24,14 @@ if TYPE_CHECKING:
     )
     from extras.graphql.filter_lookups import ExtraChoicesLookup
     from netbox.graphql.enums import ColorEnum
-    from netbox.graphql.filter_lookups import FloatLookup, IntegerLookup, JSONFilter, StringArrayLookup, TreeNodeFilter
+    from netbox.graphql.filter_lookups import (
+        BigIntegerLookup,
+        FloatLookup,
+        IntegerLookup,
+        JSONFilter,
+        StringArrayLookup,
+        TreeNodeFilter,
+    )
     from tenancy.graphql.filters import TenantFilter, TenantGroupFilter
     from users.graphql.filters import GroupFilter, UserFilter
     from virtualization.graphql.filters import ClusterFilter, ClusterGroupFilter, ClusterTypeFilter
@@ -275,6 +282,9 @@ class ImageAttachmentFilter(ChangeLoggedModelFilter):
     image_width: Annotated['IntegerLookup', strawberry.lazy('netbox.graphql.filter_lookups')] | None = (
         strawberry_django.filter_field()
     )
+    image_size: Annotated['BigIntegerLookup', strawberry.lazy('netbox.graphql.filter_lookups')] | None = (
+        strawberry_django.filter_field()
+    )
     name: StrFilterLookup | None = strawberry_django.filter_field()
 
 
diff --git a/netbox/extras/management/commands/populate_image_sizes.py b/netbox/extras/management/commands/populate_image_sizes.py
new file mode 100644
index 000000000..0a53d594c
--- /dev/null
+++ b/netbox/extras/management/commands/populate_image_sizes.py
@@ -0,0 +1,62 @@
+from django.core.management.base import BaseCommand
+
+from extras.models import ImageAttachment
+
+# Number of records to read and write per batch
+BATCH_SIZE = 100
+
+
+class Command(BaseCommand):
+    help = "Populate the image_size field for ImageAttachments that predate it"
+
+    def handle(self, *args, **options):
+        verbosity = options['verbosity']
+
+        # Only consider attachments whose size has not yet been cached. This is safe to re-run: rows whose file
+        # was unreadable on a previous run remain NULL and will be retried.
+        queryset = ImageAttachment.objects.filter(image_size__isnull=True)
+        total = queryset.count()
+
+        if not total:
+            if verbosity:
+                self.stdout.write(self.style.SUCCESS("No image attachments require updating."))
+            return
+
+        if verbosity:
+            self.stdout.write(f"Populating image_size for {total} image attachment(s)...")
+
+        updated = 0
+        skipped = 0
+        batch = []
+
+        for processed, attachment in enumerate(queryset.iterator(chunk_size=BATCH_SIZE), start=1):
+            # These rows have image_size=NULL, so the size property reads the file from storage (returning None if
+            # it's inaccessible) rather than returning a cached value.
+            size = attachment.size
+            if size is None:
+                # File is inaccessible; leave image_size NULL so a future run can retry.
+                skipped += 1
+            else:
+                attachment.image_size = size
+                batch.append(attachment)
+
+            if len(batch) >= BATCH_SIZE:
+                ImageAttachment.objects.bulk_update(batch, ['image_size'])
+                updated += len(batch)
+                batch = []
+
+            # Reading each file's size may issue a request to the storage backend, so emit periodic progress
+            # for large tables rather than going silent until completion.
+            if verbosity and processed % BATCH_SIZE == 0:
+                self.stdout.write(f"  Processed {processed}/{total}...")
+
+        if batch:
+            ImageAttachment.objects.bulk_update(batch, ['image_size'])
+            updated += len(batch)
+
+        if verbosity:
+            self.stdout.write(self.style.SUCCESS(f"Updated {updated} image attachment(s)."))
+            if skipped:
+                self.stdout.write(self.style.WARNING(
+                    f"Skipped {skipped} inaccessible file(s); re-run this command to retry them."
+                ))
diff --git a/netbox/extras/migrations/0140_imageattachment_image_size.py b/netbox/extras/migrations/0140_imageattachment_image_size.py
new file mode 100644
index 000000000..23e1f1b0b
--- /dev/null
+++ b/netbox/extras/migrations/0140_imageattachment_image_size.py
@@ -0,0 +1,16 @@
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ("extras", "0139_alter_customfieldchoiceset_extra_choices"),
+    ]
+
+    operations = [
+        migrations.AddField(
+            model_name="imageattachment",
+            name="image_size",
+            field=models.PositiveBigIntegerField(blank=True, null=True),
+        ),
+    ]
diff --git a/netbox/extras/models/models.py b/netbox/extras/models/models.py
index d538f94bf..969dbb622 100644
--- a/netbox/extras/models/models.py
+++ b/netbox/extras/models/models.py
@@ -702,6 +702,14 @@ class ImageAttachment(ChangeLoggedModel):
     image_width = models.PositiveSmallIntegerField(
         verbose_name=_('image width'),
     )
+    # Unlike image_height/image_width (populated automatically by ImageField), there is no native size_field, so
+    # this is populated in save(). It is nullable because existing rows predate the field and storage reads can
+    # fail; a null value means "not yet computed" and the size property falls back to reading storage.
+    image_size = models.PositiveBigIntegerField(
+        verbose_name=_('image size'),
+        blank=True,
+        null=True,
+    )
     name = models.CharField(
         verbose_name=_('name'),
         max_length=50,
@@ -717,6 +725,27 @@ class ImageAttachment(ChangeLoggedModel):
 
     clone_fields = ('object_type', 'object_id')
 
+    def __init__(self, *args, **kwargs):
+        super().__init__(*args, **kwargs)
+
+        # Cache an identity for the current image so save() can detect a new/replaced file and recompute the cached
+        # image_size. We combine the file name with the (auto-populated) dimensions: a replacement that reuses the
+        # same name is still caught when its dimensions differ. Read the raw image value from __dict__ to avoid
+        # triggering the ImageField descriptor here (doing so during ORM/GraphQL instantiation can recurse).
+        self._orig_image_key = self._image_identity()
+
+    def _image_identity(self):
+        """
+        Return a tuple identifying the current image file for change detection: its name plus the dimensions Django
+        populates from it. All three are read raw from __dict__ to avoid triggering the ImageField descriptor
+        (accessing `self.image` during ORM/GraphQL instantiation can recurse). Not a content fingerprint: a
+        replacement with an identical name AND identical dimensions is not distinguished (would require reading the
+        file, the storage round-trip this caching avoids).
+        """
+        original = self.__dict__.get('image')
+        name = getattr(original, 'name', original)
+        return (name, self.__dict__.get('image_height'), self.__dict__.get('image_width'))
+
     class Meta:
         ordering = ('name', 'pk')  # name may be non-unique
         indexes = (
@@ -772,12 +801,15 @@ class ImageAttachment(ChangeLoggedModel):
             alt_text=escape(self.description or self.name),
         ))
 
-    @property
-    def size(self):
+    def _read_image_size(self):
         """
-        Wrapper around `image.size` to suppress an OSError in case the file is inaccessible. Also opportunistically
-        catch other exceptions that we know other storage back-ends to throw.
+        Read the image file's size from storage, suppressing an OSError in case the file is inaccessible. Also
+        opportunistically catch other exceptions that we know other storage back-ends to throw. Returns None if the
+        size cannot be determined. This may issue a request to the storage backend (e.g. a HEAD request to S3).
         """
+        if not self.image:
+            return None
+
         expected_exceptions = [OSError]
 
         try:
@@ -791,6 +823,33 @@ class ImageAttachment(ChangeLoggedModel):
         except tuple(expected_exceptions):
             return None
 
+    @property
+    def size(self):
+        """
+        Return the size of the image file in bytes. Prefer the cached `image_size` value to avoid a storage request;
+        fall back to reading from storage for legacy rows where `image_size` has not yet been populated.
+        """
+        if self.image_size is not None:
+            return self.image_size
+        return self._read_image_size()
+
+    def save(self, *args, **kwargs):
+        # Populate image_size on creation or when the image file has changed. Reading the size may touch the storage
+        # backend (e.g. a HEAD request to S3), so we only do it when necessary: bulk operations that don't alter the
+        # image (bulk edit, rename) leave the identity unchanged and skip the read entirely. We never overwrite a good
+        # value with None (e.g. on a transient storage error); a failed read while replacing a file keeps the prior
+        # size until the next successful save, which is preferred over storing None.
+        orig_image_key = getattr(self, '_orig_image_key', None)
+        if self._state.adding or self._image_identity() != orig_image_key:
+            size = self._read_image_size()
+            if size is not None:
+                self.image_size = size
+
+        super().save(*args, **kwargs)
+
+        # Refresh the cached identity so subsequent saves on this instance detect further changes correctly.
+        self._orig_image_key = self._image_identity()
+
     def to_objectchange(self, action):
         objectchange = super().to_objectchange(action)
         objectchange.related_object = self.parent
diff --git a/netbox/extras/tests/test_api.py b/netbox/extras/tests/test_api.py
index 04ff9d424..a5f252718 100644
--- a/netbox/extras/tests/test_api.py
+++ b/netbox/extras/tests/test_api.py
@@ -774,7 +774,8 @@ class ImageAttachmentTestCase(
                 name='Image Attachment 1',
                 image='http://example.com/image1.png',
                 image_height=100,
-                image_width=100
+                image_width=100,
+                image_size=1024
             ),
             ImageAttachment(
                 object_type=ct,
@@ -782,7 +783,8 @@ class ImageAttachmentTestCase(
                 name='Image Attachment 2',
                 image='http://example.com/image2.png',
                 image_height=100,
-                image_width=100
+                image_width=100,
+                image_size=2048
             ),
             ImageAttachment(
                 object_type=ct,
@@ -790,7 +792,8 @@ class ImageAttachmentTestCase(
                 name='Image Attachment 3',
                 image='http://example.com/image3.png',
                 image_height=100,
-                image_width=100
+                image_width=100,
+                image_size=4096
             )
         )
         ImageAttachment.objects.bulk_create(image_attachments)
diff --git a/netbox/extras/tests/test_filtersets.py b/netbox/extras/tests/test_filtersets.py
index 24d3d02ef..a511f3a6c 100644
--- a/netbox/extras/tests/test_filtersets.py
+++ b/netbox/extras/tests/test_filtersets.py
@@ -741,7 +741,8 @@ class ImageAttachmentTestCase(TestCase, ChangeLoggedFilterSetTests):
                 name='Image Attachment 1',
                 image='http://example.com/image1.png',
                 image_height=100,
-                image_width=100
+                image_width=100,
+                image_size=1024
             ),
             ImageAttachment(
                 object_type=site_ct,
@@ -749,7 +750,8 @@ class ImageAttachmentTestCase(TestCase, ChangeLoggedFilterSetTests):
                 name='Image Attachment 2',
                 image='http://example.com/image2.png',
                 image_height=100,
-                image_width=100
+                image_width=100,
+                image_size=2048
             ),
             ImageAttachment(
                 object_type=rack_ct,
@@ -757,7 +759,8 @@ class ImageAttachmentTestCase(TestCase, ChangeLoggedFilterSetTests):
                 name='Image Attachment 3',
                 image='http://example.com/image3.png',
                 image_height=100,
-                image_width=100
+                image_width=100,
+                image_size=4096
             ),
             ImageAttachment(
                 object_type=rack_ct,
@@ -765,7 +768,8 @@ class ImageAttachmentTestCase(TestCase, ChangeLoggedFilterSetTests):
                 name='Image Attachment 4',
                 image='http://example.com/image4.png',
                 image_height=100,
-                image_width=100
+                image_width=100,
+                image_size=8192
             )
         )
         ImageAttachment.objects.bulk_create(image_attachments)
@@ -789,6 +793,17 @@ class ImageAttachmentTestCase(TestCase, ChangeLoggedFilterSetTests):
         }
         self.assertEqual(self.filterset(params, self.queryset).qs.count(), 1)
 
+    def test_image_size(self):
+        # Fixtures set image_size to 1024, 2048, 4096, 8192.
+        params = {'image_size': [1024, 2048]}
+        self.assertEqual(self.filterset(params, self.queryset).qs.count(), 2)
+
+    def test_image_size_range(self):
+        # __gte/__lte bound the 1024/2048/4096/8192 fixtures to the middle two. NetBox's auto-generated numeric
+        # lookups are multi-value, so values are passed as lists.
+        params = {'image_size__gte': [2048], 'image_size__lte': [4096]}
+        self.assertEqual(self.filterset(params, self.queryset).qs.count(), 2)
+
 
 class TableConfigTestCase(TestCase, ChangeLoggedFilterSetTests):
     queryset = TableConfig.objects.all()
diff --git a/netbox/extras/tests/test_management_commands.py b/netbox/extras/tests/test_management_commands.py
index 1a6e2bfe8..3372de375 100644
--- a/netbox/extras/tests/test_management_commands.py
+++ b/netbox/extras/tests/test_management_commands.py
@@ -11,6 +11,8 @@ from dcim.choices import InterfaceTypeChoices
 from dcim.models import Device, DeviceRole, DeviceType, Interface, Manufacturer, Site
 from extras.management.commands import renaturalize, webhook_receiver
 from extras.management.commands.webhook_receiver import WebhookHandler
+from extras.models import ImageAttachment
+from extras.tests.test_models import OverwriteStyleMemoryStorage, UnreadableSizeMemoryStorage
 from users.models import User
 from utilities.fields import NaturalOrderingField
 
@@ -502,3 +504,65 @@ class WebhookReceiverTestCase(TestCase):
 
         print_.assert_any_call('(No body)')
         print_.assert_any_call('Completed request #1')
+
+
+class PopulateImageSizesTestCase(TestCase):
+    @classmethod
+    def setUpTestData(cls):
+        cls.ct_site = ContentType.objects.get_by_natural_key('dcim', 'site')
+        cls.site = Site.objects.create(name='Site 1', slug='site-1')
+
+    def _legacy_attachment(self, name, image_name):
+        # bulk_create skips save(), so image_size starts NULL, mimicking a row created before the field existed.
+        attachment = ImageAttachment(
+            object_type=self.ct_site,
+            object_id=self.site.pk,
+            name=name,
+            image=image_name,
+            image_height=100,
+            image_width=100,
+        )
+        ImageAttachment.objects.bulk_create([attachment])
+        return ImageAttachment.objects.get(name=name)
+
+    def test_populates_null_image_sizes(self):
+        field = ImageAttachment._meta.get_field('image')
+        storage = OverwriteStyleMemoryStorage()
+        storage.files['image-attachments/site_1_a.png'] = b'\x00' * 321
+
+        attachment = self._legacy_attachment('Legacy 1', 'image-attachments/site_1_a.png')
+        self.assertIsNone(attachment.image_size)
+
+        out = StringIO()
+        with patch.object(field, 'storage', storage):
+            call_command('populate_image_sizes', stdout=out)
+            # Read the persisted value back under the patched storage (refreshing the image field re-reads
+            # dimensions from storage, which must be the in-memory backend).
+            persisted = ImageAttachment.objects.get(pk=attachment.pk)
+            self.assertEqual(persisted.image_size, 321)
+
+        self.assertIn('Updated 1', out.getvalue())
+
+    def test_skips_unreadable_files_and_is_rerunnable(self):
+        field = ImageAttachment._meta.get_field('image')
+        attachment = self._legacy_attachment('Legacy 2', 'image-attachments/site_1_missing.png')
+
+        # First run: storage can't report size, so the row is skipped and left NULL.
+        out = StringIO()
+        with patch.object(field, 'storage', UnreadableSizeMemoryStorage()):
+            call_command('populate_image_sizes', stdout=out)
+            self.assertIsNone(ImageAttachment.objects.get(pk=attachment.pk).image_size)
+        self.assertIn('Skipped 1', out.getvalue())
+
+        # Second run: storage now works, and the previously-skipped row is picked up.
+        storage = OverwriteStyleMemoryStorage()
+        storage.files['image-attachments/site_1_missing.png'] = b'\x00' * 654
+        out = StringIO()
+        with patch.object(field, 'storage', storage):
+            call_command('populate_image_sizes', stdout=out)
+            self.assertEqual(ImageAttachment.objects.get(pk=attachment.pk).image_size, 654)
+
+    def test_noop_when_nothing_to_update(self):
+        out = StringIO()
+        call_command('populate_image_sizes', stdout=out)
+        self.assertIn('No image attachments require updating.', out.getvalue())
diff --git a/netbox/extras/tests/test_models.py b/netbox/extras/tests/test_models.py
index a3945f282..e55304cbd 100644
--- a/netbox/extras/tests/test_models.py
+++ b/netbox/extras/tests/test_models.py
@@ -74,6 +74,16 @@ class OverwriteStyleMemoryStorage(Storage):
         return f'https://example.invalid/{name}'
 
 
+class UnreadableSizeMemoryStorage(OverwriteStyleMemoryStorage):
+    """
+    Like OverwriteStyleMemoryStorage, but size() raises OSError to model a storage backend that is
+    transiently unavailable (e.g. an S3 outage) when reading file size.
+    """
+
+    def size(self, name):
+        raise OSError('storage unavailable')
+
+
 class ImageAttachmentTestCase(TestCase):
     @classmethod
     def setUpTestData(cls):
@@ -191,6 +201,204 @@ class ImageAttachmentTestCase(TestCase):
 
         self.assertCountEqual(storage.files.keys(), {base_name, suffixed_name})
 
+    def test_save_populates_image_size_on_create(self):
+        """
+        save() populates image_size from the uploaded file on creation.
+        """
+        storage = OverwriteStyleMemoryStorage()
+        field = ImageAttachment._meta.get_field('image')
+
+        with patch.object(field, 'storage', storage):
+            ia = ImageAttachment(
+                object_type=self.ct_site,
+                object_id=self.site.pk,
+                image=self._uploaded_png('size-on-create.png'),
+            )
+            ia.save()
+
+            self.assertIsNotNone(ia.image_size)
+            self.assertEqual(ia.image_size, ia.image.size)
+
+    def test_size_property_returns_stored_value_without_storage_access(self):
+        """
+        The size property returns the cached image_size rather than the file's actual size. The stub's empty
+        file reports size 0, so asserting the distinct stored value proves the property used the cached value.
+        """
+        ia = self._stub_image_attachment(self.site.pk, 'image-attachments/site_1_no-file.png')
+        self.assertEqual(ia._read_image_size(), 0)  # the stub's empty file genuinely reports 0
+        ia.image_size = 9999
+
+        self.assertEqual(ia.size, 9999)
+
+    def test_size_property_falls_back_to_storage_when_unset(self):
+        """
+        For legacy rows where image_size is NULL, the size property falls back to reading storage
+        (rather than reporting 0 bytes).
+        """
+        storage = OverwriteStyleMemoryStorage()
+        field = ImageAttachment._meta.get_field('image')
+
+        with patch.object(field, 'storage', storage):
+            ia = ImageAttachment(
+                object_type=self.ct_site,
+                object_id=self.site.pk,
+                image=self._uploaded_png('fallback.png'),
+            )
+            ia.save()
+
+            # Simulate a legacy row that predates the image_size field.
+            ia.image_size = None
+            self.assertEqual(ia.size, ia.image.size)
+            self.assertGreater(ia.size, 0)
+
+    def test_save_does_not_clobber_existing_size_on_storage_error(self):
+        """
+        When the storage backend raises on a size read (modeled by a real Storage subclass, not a mock),
+        save() must not overwrite an existing image_size with None.
+        """
+        field = ImageAttachment._meta.get_field('image')
+
+        # Create a row with a real, readable size.
+        with patch.object(field, 'storage', OverwriteStyleMemoryStorage()):
+            ia = ImageAttachment(
+                object_type=self.ct_site,
+                object_id=self.site.pk,
+                image=self._uploaded_png('keep-size.png'),
+            )
+            ia.save()
+            original_size = ia.image_size
+            self.assertIsNotNone(original_size)
+
+        # Reload from the DB so the FieldFile has no cached size and must consult storage (as it would for a
+        # row loaded fresh in production). With the backend unable to report size, the read fails (returns None),
+        # and save() must keep the previously-stored value rather than clobbering it with None.
+        with patch.object(field, 'storage', UnreadableSizeMemoryStorage()):
+            reloaded = ImageAttachment.objects.get(pk=ia.pk)
+            self.assertIsNone(reloaded._read_image_size())  # the read genuinely fails (returns None)
+            # Make the image look replaced by perturbing the cached identity (different name component).
+            reloaded._orig_image_key = ('image-attachments/site_1_old.png', reloaded.image_height, reloaded.image_width)
+            reloaded.save()
+
+            # In-memory value is preserved, and the persisted value is unchanged.
+            self.assertEqual(reloaded.image_size, original_size)
+            self.assertEqual(ImageAttachment.objects.get(pk=ia.pk).image_size, original_size)
+
+    def test_save_recomputes_image_size_when_image_replaced(self):
+        """
+        Replacing the image on an existing row recomputes image_size (Cable-style change detection).
+        """
+        storage = OverwriteStyleMemoryStorage()
+        field = ImageAttachment._meta.get_field('image')
+
+        with patch.object(field, 'storage', storage):
+            ia = ImageAttachment(
+                object_type=self.ct_site,
+                object_id=self.site.pk,
+                image=self._uploaded_png('original.png'),
+            )
+            ia.save()
+            original_size = ia.image_size
+            self.assertIsNotNone(original_size)
+
+            # Replace the image with a larger file and save again.
+            larger = SimpleUploadedFile(
+                name='replacement.png',
+                content=self._uploaded_png('replacement.png').read() + b'\x00' * 100,
+                content_type='image/png',
+            )
+            ia.image = larger
+            ia.save()
+
+            self.assertEqual(ia.image_size, ia.image.size)
+            self.assertNotEqual(ia.image_size, original_size)
+
+    def test_image_identity_includes_dimensions(self):
+        """
+        The change-detection key combines the image name with its dimensions, so a replacement that reuses the
+        same name but changes dimensions produces a different key (which name alone would not).
+        """
+        ia = self._stub_image_attachment(self.site.pk, 'image-attachments/site_1_same.png')
+        ia.image_height, ia.image_width = 10, 10
+        key_small = ia._image_identity()
+
+        # Same name, different dimensions (as Django would set when a same-named file is replaced).
+        ia.image_height, ia.image_width = 40, 40
+        key_large = ia._image_identity()
+
+        self.assertEqual(key_small[0], key_large[0])   # name component unchanged
+        self.assertNotEqual(key_small, key_large)      # but the key differs, so save() will recompute
+
+    def test_save_recomputes_image_size_when_dimensions_change_under_same_name(self):
+        """
+        When the image is replaced by a file with the same stored name but different dimensions, save()
+        recomputes image_size. Name-only detection would miss this; the dimension component catches it.
+        Simulates the same-name case by priming the cached identity with the old dimensions.
+        """
+        storage = OverwriteStyleMemoryStorage()
+        field = ImageAttachment._meta.get_field('image')
+
+        with patch.object(field, 'storage', storage):
+            ia = ImageAttachment(
+                object_type=self.ct_site,
+                object_id=self.site.pk,
+                image=self._uploaded_png('same-name.png'),
+            )
+            ia.save()
+            name = ia.image.name
+
+            # Force the cached identity to reflect the SAME name but different (old) dimensions, then bump the
+            # current dimensions to mimic a same-name replacement with a differently-sized image.
+            ia._orig_image_key = (name, ia.image_height + 5, ia.image_width + 5)
+            ia.save()
+
+            self.assertEqual(ia.image.name, name)                 # name unchanged
+            self.assertEqual(ia.image_size, ia.image.size)        # size recomputed despite same name
+
+    def test_save_without_touching_image_does_not_recompute_or_read_storage(self):
+        """
+        Editing an existing row without replacing the image leaves image_size untouched and does not
+        hit storage. Directly guards against the change-detection comparison misfiring.
+        """
+        storage = OverwriteStyleMemoryStorage()
+        field = ImageAttachment._meta.get_field('image')
+
+        with patch.object(field, 'storage', storage):
+            ia = ImageAttachment(
+                object_type=self.ct_site,
+                object_id=self.site.pk,
+                name='Original',
+                image=self._uploaded_png('untouched.png'),
+            )
+            ia.save()
+            stored_size = ia.image_size
+
+            # Reload from the DB so the cached image identity is set from the persisted value, then edit only the name.
+            reloaded = ImageAttachment.objects.get(pk=ia.pk)
+            reloaded.name = 'Renamed'
+            with patch.object(ImageAttachment, '_read_image_size', side_effect=AssertionError('storage accessed')):
+                reloaded.save()
+
+            self.assertEqual(reloaded.image_size, stored_size)
+
+    def test_save_populates_image_size_via_constructor_kwarg(self):
+        """
+        The non-UI create path (constructor kwarg / REST / bulk) populates image_size correctly,
+        confirming change detection behaves when image is passed as a FieldFile.
+        """
+        storage = OverwriteStyleMemoryStorage()
+        field = ImageAttachment._meta.get_field('image')
+
+        with patch.object(field, 'storage', storage):
+            ia = ImageAttachment(
+                object_type=self.ct_site,
+                object_id=self.site.pk,
+                image=self._uploaded_png('kwarg.png'),
+            )
+            ia.save()
+
+            self.assertIsNotNone(ia.image_size)
+            self.assertEqual(ia.image_size, ia.image.size)
+
 
 class TableConfigTestCase(TestCase):
     @classmethod
diff --git a/netbox/extras/tests/test_views.py b/netbox/extras/tests/test_views.py
index 15434b0f2..f04e96bba 100644
--- a/netbox/extras/tests/test_views.py
+++ b/netbox/extras/tests/test_views.py
@@ -481,6 +481,7 @@ class ImageAttachmentTestCase(
                     image='http://example.com/image1.png',
                     image_height=100,
                     image_width=100,
+                    image_size=1024,
                 ),
                 ImageAttachment(
                     object_type=ct,
@@ -489,6 +490,7 @@ class ImageAttachmentTestCase(
                     image='http://example.com/image2.png',
                     image_height=100,
                     image_width=100,
+                    image_size=2048,
                 ),
                 ImageAttachment(
                     object_type=ct,
@@ -497,6 +499,7 @@ class ImageAttachmentTestCase(
                     image='http://example.com/image3.png',
                     image_height=100,
                     image_width=100,
+                    image_size=4096,
                 ),
             ]
         )