diff --git a/backend/bun.lock b/backend/bun.lock
index cc33ee5..1b33ca5 100644
--- a/backend/bun.lock
+++ b/backend/bun.lock
@@ -5,6 +5,7 @@
     "": {
       "name": "hono",
       "dependencies": {
+        "file-type": "^22.1.1",
         "hono": "^4.13.10",
       },
       "devDependencies": {
@@ -16,6 +17,12 @@
     },
   },
   "packages": {
+    "@borewit/text-codec": ["@borewit/text-codec@0.2.2", "", {}, "sha512-DDaRehssg1aNrH4+2hnj1B7vnUGEjU6OIlyRdkMd0aUdIUvKXrJfXsy8LVtXAy7DRvYVluWbMspsRhz2lcW0mQ=="],
+
+    "@tokenizer/inflate": ["@tokenizer/inflate@0.4.1", "", { "dependencies": { "debug": "^4.4.3", "token-types": "^6.1.1" } }, "sha512-2mAv+8pkG6GIZiF1kNg1jAjh27IDxEPKwdGul3snfztFerfPGI1LjDezZp3i7BElXompqEtPmoPx6c2wgtWsOA=="],
+
+    "@tokenizer/token": ["@tokenizer/token@0.3.0", "", {}, "sha512-OvjF+z51L3ov0OyAU0duzsYuvO01PH7x4t6DJx+guahgTnBHkhJdG7soQeTSFLWN3efnHyibZ4Z8l2EuWwJN3A=="],
+
     "@types/bun": ["@types/bun@1.4.2", "", { "dependencies": { "bun-types": "1.4.2" } }, "sha512-GimotNn7+ZV0uVArItBbriZsR1oNf0+WTzPkdcFrzShI7k2norL0uzEaJT8T33dWr7O/c9ZDuAFQrctKCi72oQ=="],
 
     "@types/node": ["@types/node@26.6.3", "", { "dependencies": { "undici-types": "~8.9.0" } }, "sha512-dsqMQQoeTLqu9wynDD00q573mNzso3IdQOAfHRJqLCcmCFPoGo9A1bDpUcv/9tnKpErQWv9uKeGfl37EIS02Yg=="],
@@ -62,10 +69,24 @@
 
     "bun-types": ["bun-types@1.4.2", "", { "dependencies": { "@types/node": "*" } }, "sha512-bxV1FgK7yBIzjRe5zBozIM4Bem11ZJcCXSrjWRG3YWLt8yFDePu4cLjpebO8OvPeIE9trbyPF4fuj3Cia4Fj3w=="],
 
+    "debug": ["debug@4.4.3", "", { "dependencies": { "ms": "^2.1.3" }, "peerDependencies": { "supports-color": "*" }, "optionalPeers": ["supports-color"] }, "sha512-RGwwWnwQvkVfavKVt22FGLw+xYSdzARwm0ru6DhTVA3umU5hZc28V3kO4stgYryrTlLpuvgI9GiijltAjNbcqA=="],
+
+    "file-type": ["file-type@22.1.1", "", { "dependencies": { "@tokenizer/inflate": "^0.4.1", "strtok3": "^10.3.5", "token-types": "^6.1.2", "uint8array-extras": "^1.5.0" } }, "sha512-sEB0oStmeLGtpmSAD88RDNuLsvhv4iC3u0lE25CUvfCULvj49xoQ3l3K525Vn+ZzsZ6DOLajQCV6RmhwwhqiJg=="],
+
     "hono": ["hono@4.13.10", "", {}, "sha512-dQuLsa5oO+47QVMVMaaD9cIv8ctmVtK1iRvwWngkfloFJMeFeuoUFDswIqZGxmGX3hrRzREgEArjkK9OgsQEhA=="],
 
+    "ieee754": ["ieee754@1.2.1", "", {}, "sha512-dcyqhDvX1C46lXZcVqCpK+FtMRQVdIMN6/Df5js2zouUsqG7I6sFxitIC+7KYK29KdXOLHdu9zL4sFnoVQnqaA=="],
+
+    "ms": ["ms@2.1.3", "", {}, "sha512-6FlzubTLZG3J2a/NVCAleEhjzq5oxgHyaCU9yYXvcLsvoVaHJq/s5xXI6/XXP6tz7R9xAOtHnSO/tXtF3WRTlA=="],
+
+    "strtok3": ["strtok3@10.3.5", "", { "dependencies": { "@tokenizer/token": "^0.3.0" } }, "sha512-ki4hZQfh5rX0QDLLkOCj+h+CVNkqmp/CMf8v8kZpkNVK6jGQooMytqzLZYUVYIZcFZ6yDB70EfD8POcFXiF5oA=="],
+
+    "token-types": ["token-types@6.1.2", "", { "dependencies": { "@borewit/text-codec": "^0.2.1", "@tokenizer/token": "^0.3.0", "ieee754": "^1.2.1" } }, "sha512-dRXchy+C0IgK8WPC6xvCHFRIWYUbqqdEIKPaKo/AcTUNzwLTK6AH7RjdLWsEZcAN/TBdtfUw3PYEgPr5VPr6ww=="],
+
     "typescript": ["typescript@7.0.2", "", { "optionalDependencies": { "@typescript/typescript-aix-ppc64": "7.0.2", "@typescript/typescript-darwin-arm64": "7.0.2", "@typescript/typescript-darwin-x64": "7.0.2", "@typescript/typescript-freebsd-arm64": "7.0.2", "@typescript/typescript-freebsd-x64": "7.0.2", "@typescript/typescript-linux-arm": "7.0.2", "@typescript/typescript-linux-arm64": "7.0.2", "@typescript/typescript-linux-loong64": "7.0.2", "@typescript/typescript-linux-mips64el": "7.0.2", "@typescript/typescript-linux-ppc64": "7.0.2", "@typescript/typescript-linux-riscv64": "7.0.2", "@typescript/typescript-linux-s390x": "7.0.2", "@typescript/typescript-linux-x64": "7.0.2", "@typescript/typescript-netbsd-arm64": "7.0.2", "@typescript/typescript-netbsd-x64": "7.0.2", "@typescript/typescript-openbsd-arm64": "7.0.2", "@typescript/typescript-openbsd-x64": "7.0.2", "@typescript/typescript-sunos-x64": "7.0.2", "@typescript/typescript-win32-arm64": "7.0.2", "@typescript/typescript-win32-x64": "7.0.2" }, "bin": { "tsc": "bin/tsc" } }, "sha512-8FYau96o3NKOhbjKi/qNvG/W5jhzxkbdm5sj9AbZ/5T5sWqn3hJgLfGx27sRKZWTvyzCP8dLRBTf5tBTSRVUNA=="],
 
+    "uint8array-extras": ["uint8array-extras@1.6.0", "", {}, "sha512-8iAasVS4wUx0gPLjH8Xtz2PeDzTSiy8QiLGu2DT3X5GU+egFEQhpnbtkehbAwjvDcxIERmCYcysiODFmE3Ud0Q=="],
+
     "undici-types": ["undici-types@8.9.0", "", {}, "sha512-KTDyRTYX8sWmKXAikPHHSyc63CRPETMctyjKFupcC6OBLXT3xsN0e9aF7m+mIXutFWpUXuedtowG7iLOzp0kQg=="],
   }
 }
diff --git a/backend/package.json b/backend/package.json
index b7cff30..3c6d884 100644
--- a/backend/package.json
+++ b/backend/package.json
@@ -13,6 +13,7 @@
   },
   "type": "module",
   "dependencies": {
+    "file-type": "^22.1.1",
     "hono": "^4.13.10"
   }
 }
diff --git a/backend/src/index.ts b/backend/src/index.ts
index 614e27b..f08f4e0 100644
--- a/backend/src/index.ts
+++ b/backend/src/index.ts
@@ -1,3 +1,4 @@
+import { fileTypeFromBuffer } from "file-type";
 import { Hono } from "hono";
 import { validator } from "hono/validator";
 
@@ -28,7 +29,7 @@ const app = appTmp.basePath("/watermark")
  * param: outputType: 输出的文件类型，只允许 jpeg | png
  */
 app.post("/encode",
-    validator("form", (val, c) => {
+    validator("form", async (val, c) => {
         const image = val.image
         const payload = val.payload
         const strength = val.strength
@@ -62,6 +63,26 @@ app.post("/encode",
             })
         }
 
+        // 通过魔术数字判断文件真实类型
+        const imageBuffer = await (image as File).arrayBuffer()
+        const unit8Image = new Uint8Array(imageBuffer)
+        const imageType = await fileTypeFromBuffer(unit8Image)
+        if (!imageType) {
+            c.status(400)
+            return c.json({
+                code: 400,
+                msg: "Image type is invalid, must be jpeg or png"
+            })
+        }
+        if (!["image/png", "image/jpeg"].includes(imageType.mime)) {
+            c.status(400)
+            return c.json({
+                code: 400,
+                msg: "Image type is invalid, must be jpeg or png"
+            })
+        }
+        // DONE
+
         const MAX_IMAGE_SIZE = 10 * 1024 * 1024
         if ((image as File).size > MAX_IMAGE_SIZE) {
             c.status(400)