From 420c8c77be5c4231ff747ceb07114d01eb690df5 Mon Sep 17 00:00:00 2001
From: "xy.kong" <xy.kong@gmail.com>
Date: Wed, 1 Apr 2026 14:27:15 +0800
Subject: [PATCH] fix(anthropic): auto-detect image media_type from magic bytes

Anthropic API rejects requests where the declared media_type in the
data URI prefix (e.g. 'data:image/png;base64,...') does not match the
actual image bytes, returning:
  'The image was specified using the image/png media type, but the
   image appears to be a image/jpeg image'

convert_to_anthropic_image_obj() trusted the declared type from the
data URI without verifying it against the actual bytes. Now it decodes
the first 128 bytes and runs them through the existing get_image_type()
magic-byte detector. If the detected MIME type differs, the detected
type is used. Detection failure falls back to the declared type
gracefully.

Fixes #24900
---
 .../prompt_templates/factory.py               | 20 +++++++++++++++++++
 1 file changed, 20 insertions(+)

diff --git a/litellm/litellm_core_utils/prompt_templates/factory.py b/litellm/litellm_core_utils/prompt_templates/factory.py
index d29ca1649ff..38a8856d8f4 100644
--- a/litellm/litellm_core_utils/prompt_templates/factory.py
+++ b/litellm/litellm_core_utils/prompt_templates/factory.py
@@ -898,6 +898,26 @@ def convert_to_anthropic_image_obj(
         else:
             media_type = media_type.replace("\\/", "/")
 
+        # Anthropic rejects requests where the declared media_type mismatches the actual
+        # image bytes. Auto-detect from magic bytes and override the declared type when needed.
+        try:
+            from litellm.litellm_core_utils.token_counter import get_image_type
+
+            image_bytes = base64.b64decode(base64_data[:128])
+            detected = get_image_type(image_bytes)
+            if detected is not None:
+                detected_mime = "image/{}".format(detected)
+                if detected_mime != media_type:
+                    verbose_logger.debug(
+                        "convert_to_anthropic_image_obj: declared media_type=%s does not match "
+                        "detected type=%s; using detected type.",
+                        media_type,
+                        detected_mime,
+                    )
+                    media_type = detected_mime
+        except Exception:
+            pass
+
         return GenericImageParsingChunk(
             type="base64",
             media_type=media_type,