diff --git a/backend/open_webui/routers/openai.py b/backend/open_webui/routers/openai.py
index e5c9f2e7e8..2e93d47e41 100644
--- a/backend/open_webui/routers/openai.py
+++ b/backend/open_webui/routers/openai.py
@@ -1092,8 +1092,13 @@ def convert_to_responses_payload(payload: dict) -> dict:
                     content_parts.append({'type': text_type, 'text': part.get('text', '')})
                 elif part.get('type') == 'image_url':
                     url_data = part.get('image_url', {})
-                    url = url_data.get('url', '') if isinstance(url_data, dict) else url_data
-                    content_parts.append({'type': 'input_image', 'image_url': url})
+                    if isinstance(url_data, dict):
+                        url = url_data.get('url', '')
+                        detail = url_data.get('detail') or 'auto'
+                    else:
+                        url = url_data
+                        detail = 'auto'
+                    content_parts.append({'type': 'input_image', 'image_url': url, 'detail': detail})
         else:
             content_parts = [{'type': text_type, 'text': str(content)}]
 
diff --git a/backend/test/routers/test_openai.py b/backend/test/routers/test_openai.py
new file mode 100644
index 0000000000..851e775482
--- /dev/null
+++ b/backend/test/routers/test_openai.py
@@ -0,0 +1,40 @@
+from copy import deepcopy
+
+from open_webui.routers.openai import convert_to_responses_payload
+
+
+def _convert(image_url: object) -> dict:
+    payload = {
+        'messages': [
+            {
+                'role': 'user',
+                'content': [{'type': 'image_url', 'image_url': image_url}],
+            }
+        ]
+    }
+    result = convert_to_responses_payload(deepcopy(payload))
+    return result['input'][0]['content'][0]
+
+
+def test_image_object_without_detail_defaults_to_auto() -> None:
+    assert _convert({'url': 'data:image/png;base64,abc'}) == {
+        'type': 'input_image',
+        'image_url': 'data:image/png;base64,abc',
+        'detail': 'auto',
+    }
+
+
+def test_image_object_preserves_explicit_detail() -> None:
+    assert _convert({'url': 'https://example.test/image.png', 'detail': 'high'}) == {
+        'type': 'input_image',
+        'image_url': 'https://example.test/image.png',
+        'detail': 'high',
+    }
+
+
+def test_string_image_url_defaults_to_auto() -> None:
+    assert _convert('https://example.test/image.png') == {
+        'type': 'input_image',
+        'image_url': 'https://example.test/image.png',
+        'detail': 'auto',
+    }