diff --git a/extensions/qqbot/src/engine/gateway/inbound-attachments.test.ts b/extensions/qqbot/src/engine/gateway/inbound-attachments.test.ts
index 970ea535886..e9eb0545eca 100644
--- a/extensions/qqbot/src/engine/gateway/inbound-attachments.test.ts
+++ b/extensions/qqbot/src/engine/gateway/inbound-attachments.test.ts
@@ -73,6 +73,58 @@ describe("engine/gateway/inbound-attachments", () => {
     expect(result.attachmentLocalPaths).toEqual([null]);
   });
 
+  it("classifies image content types case-insensitively when download succeeds", async () => {
+    downloadFileMock.mockResolvedValueOnce("/tmp/openclaw-qqbot-downloads/a.png");
+    downloadFileMock.mockResolvedValueOnce("/tmp/openclaw-qqbot-downloads/b.png");
+
+    const result = await processAttachments(
+      [
+        { content_type: "image/png", url: "https://cdn.example.test/a.png", filename: "a.png" },
+        { content_type: "Image/PNG", url: "https://cdn.example.test/b.png", filename: "b.png" },
+      ],
+      { accountId: "qq", cfg: {}, audioConvert },
+    );
+
+    expect(result.imageUrls).toEqual([
+      "/tmp/openclaw-qqbot-downloads/a.png",
+      "/tmp/openclaw-qqbot-downloads/b.png",
+    ]);
+    // The raw content_type passes through unchanged.
+    expect(result.imageMediaTypes).toEqual(["image/png", "Image/PNG"]);
+    expect(result.attachmentInfo).toBe("");
+  });
+
+  it("uses the remote image URL for a mixed-case image content type when download fails", async () => {
+    downloadFileMock.mockResolvedValue(null);
+
+    const result = await processAttachments(
+      [{ content_type: "Image/PNG", url: "//cdn.example.test/a.png", filename: "a.png" }],
+      { accountId: "qq", cfg: {}, audioConvert },
+    );
+
+    expect(result.imageUrls).toEqual(["https://cdn.example.test/a.png"]);
+    expect(result.imageMediaTypes).toEqual(["Image/PNG"]);
+    expect(result.attachmentLocalPaths).toEqual([null]);
+  });
+
+  it("does not classify a mixed-case non-image content type as an image", async () => {
+    downloadFileMock.mockResolvedValue("/tmp/openclaw-qqbot-downloads/doc.pdf");
+
+    const result = await processAttachments(
+      [
+        {
+          content_type: "Application/PDF",
+          url: "https://cdn.example.test/doc.pdf",
+          filename: "doc.pdf",
+        },
+      ],
+      { accountId: "qq", cfg: {}, audioConvert },
+    );
+
+    expect(result.imageUrls).toEqual([]);
+    expect(result.attachmentInfo).toBe("\n[Attachment: /tmp/openclaw-qqbot-downloads/doc.pdf]");
+  });
+
   it("prefers voice_wav_url for voice downloads and transcribes with configured STT", async () => {
     downloadFileMock.mockResolvedValue("/tmp/openclaw-qqbot-downloads/voice.wav");
     resolveSTTConfigMock.mockReturnValue({
diff --git a/extensions/qqbot/src/engine/gateway/inbound-attachments.ts b/extensions/qqbot/src/engine/gateway/inbound-attachments.ts
index 3a634588518..20f57d65910 100644
--- a/extensions/qqbot/src/engine/gateway/inbound-attachments.ts
+++ b/extensions/qqbot/src/engine/gateway/inbound-attachments.ts
@@ -3,7 +3,10 @@ import { truncateUtf16Safe } from "openclaw/plugin-sdk/text-utility-runtime";
 import type { AudioConvertPort } from "../adapter/audio.port.js";
 import { downloadFile } from "../utils/file-utils.js";
 import { getQQBotMediaDir } from "../utils/platform.js";
-import { normalizeOptionalString } from "../utils/string-normalize.js";
+import {
+  normalizeLowercaseStringOrEmpty,
+  normalizeOptionalString,
+} from "../utils/string-normalize.js";
 import { transcribeAudio, resolveSTTConfig } from "../utils/stt.js";
 
 // Re-export the port type for convenience.
@@ -115,6 +118,10 @@ export async function processAttachments(
   const processTasks = downloadResults.map(
     async ({ att, attUrl, isVoice, localPath, audioPath }) => {
       const asrReferText = normalizeOptionalString(att.asr_refer_text) ?? "";
+      // MIME types are case-insensitive (RFC 2045) and relays may emit
+      // mixed-case values; compare lowercased but keep the raw content_type
+      // in returned fields.
+      const normalizedContentType = normalizeLowercaseStringOrEmpty(att.content_type);
       const wavUrl =
         isVoice && att.voice_wav_url
           ? att.voice_wav_url.startsWith("//")
@@ -129,7 +136,7 @@ export async function processAttachments(
       };
 
       if (localPath) {
-        if (att.content_type?.startsWith("image/")) {
+        if (normalizedContentType.startsWith("image/")) {
           log?.debug?.(`Downloaded attachment to: ${localPath}`);
           return { localPath, type: "image" as const, contentType: att.content_type, meta };
         }
@@ -150,7 +157,7 @@ export async function processAttachments(
         return { localPath, type: "other" as const, filename: att.filename, meta };
       }
       log?.error(`Failed to download: ${attUrl}`);
-      if (att.content_type?.startsWith("image/")) {
+      if (normalizedContentType.startsWith("image/")) {
         return {
           localPath: null,
           type: "image-fallback" as const,
diff --git a/extensions/qqbot/src/engine/utils/audio.test.ts b/extensions/qqbot/src/engine/utils/audio.test.ts
index a3010f67fb0..86cacbb5251 100644
--- a/extensions/qqbot/src/engine/utils/audio.test.ts
+++ b/extensions/qqbot/src/engine/utils/audio.test.ts
@@ -97,6 +97,12 @@ describe("engine/utils/audio", () => {
       expect(isVoiceAttachment({ filename: "msg.slac" })).toBe(true);
     });
 
+    it("treats content_type case-insensitively", () => {
+      expect(isVoiceAttachment({ content_type: "Voice" })).toBe(true);
+      expect(isVoiceAttachment({ content_type: "Audio/Silk" })).toBe(true);
+      expect(isVoiceAttachment({ content_type: "Image/PNG" })).toBe(false);
+    });
+
     it("rejects non-voice attachments", () => {
       expect(isVoiceAttachment({ content_type: "image/png" })).toBe(false);
       expect(isVoiceAttachment({ filename: "photo.jpg" })).toBe(false);
diff --git a/extensions/qqbot/src/engine/utils/audio.ts b/extensions/qqbot/src/engine/utils/audio.ts
index 04cea695c98..1718d20a1f1 100644
--- a/extensions/qqbot/src/engine/utils/audio.ts
+++ b/extensions/qqbot/src/engine/utils/audio.ts
@@ -118,7 +118,11 @@ export async function convertSilkToWav(
 
 /** Check whether an attachment is a voice file (by MIME type or extension). */
 export function isVoiceAttachment(att: { content_type?: string; filename?: string }): boolean {
-  if (att.content_type === "voice" || att.content_type?.startsWith("audio/")) {
+  // MIME types are case-insensitive (RFC 2045) and relays may emit mixed-case
+  // values; the bare "voice" platform sentinel gets the same treatment.
+  // Compare lowercased like the extension check below.
+  const contentType = normalizeLowercase(att.content_type);
+  if (contentType === "voice" || contentType.startsWith("audio/")) {
     return true;
   }
   const ext = att.filename ? normalizeLowercase(path.extname(att.filename)) : "";