diff --git a/backend/src/index.ts b/backend/src/index.ts
index d6227d0..72d0035 100644
--- a/backend/src/index.ts
+++ b/backend/src/index.ts
@@ -33,6 +33,14 @@ app.post("/encode",
             })
         }
 
+        if ((image as File[]).length >= 2) {
+            c.status(400)
+            return c.json({
+                code: 400,
+                msg: "Only support upload one image"
+            })
+        }
+
         if ((image as File).size == 0) {
             c.status(400)
             return c.json({
@@ -130,6 +138,77 @@ app.post("/encode",
         return c.body(resImage)
     })
 
+app.post("/decode",
+    validator("form", (val, c) => {
+        const image = val.image
+        if (image == undefined) {
+            c.status(400)
+            return c.json({
+                code: 400,
+                msg: "Paarameter is invalid"
+            })
+        }
+
+        if ((image as File[]).length >= 2) {
+            c.status(400)
+            return c.json({
+                code: 400,
+                msg: "Only support upload one image"
+            })
+        }
+
+        if ((image as File).size == 0) {
+            c.status(400)
+            return c.json({
+                code: 400,
+                msg: "Image is empty"
+            })
+        }
+
+        const MAX_IMAGE_SIZE = 10 * 1024 * 1024
+        if ((image as File).size > MAX_IMAGE_SIZE) {
+            c.status(400)
+            return c.json({
+                code: 400,
+                msg: "Image size is too large, must<=10MB"
+            })
+        }
+    },),
+    async (c) => {
+        const formData = await c.req.formData()
+        const image: File = formData.get("image") as File
+        const data = new FormData()
+        let canFetch: boolean = true
+        data.append("image", image)
+
+        const response = await fetch("http://localhost:8081/watermark/decode", {
+            method: "POST",
+            body: data
+        }).catch((e) => {
+            canFetch = false
+        })
+
+        if (!canFetch) {
+            c.status(500)
+            return c.json({
+                code: 500,
+                msg: "Cannot fetch http://localhost:8081/watermark/decode"
+            })
+        }
+
+        const res = await response!.json()
+        /**
+         * Response struct
+         * {
+         *      "hasWatermark": true|false,
+         *      "payload": "abc" | null,
+         *      "schema": 1 | null
+         *  }
+         */
+        return c.body(JSON.stringify(res))
+    }
+)
+
 export default {
     port: 8080,
     fetch: app.fetch