diff --git a/app/api/users.py b/app/api/users.py
index 043dd98..241e08f 100644
--- a/app/api/users.py
+++ b/app/api/users.py
@@ -1,28 +1,54 @@
-from fastapi import APIRouter, File, Form, UploadFile
+from fastapi import APIRouter, File, Form, UploadFile, HTTPException
 from app.models.user import UserResponse
 
+from app.services.user_service import (
+    authenticate_user,
+    delete_user,
+    get_user,   
+    register_user,
+)
+
 router = APIRouter()
 
 
 @router.post("/users/register", response_model=UserResponse)
 async def register(user_id: str = Form(...), image: UploadFile = File(...)):
     """회원 등록 엔드포인트"""
-    pass
+    image_data = await image.read()
+    registered_user = register_user(user_id, image_data)
+
+    return UserResponse(
+        user_id=registered_user["user_id"],
+        registered_at=registered_user["registered_at"],
+    )
 
 
 @router.post("/users/authenticate")
 async def authenticate(image: UploadFile = File(...)):
     """회원 인증 엔드포인트"""
-    pass
+    image_data = await image.read()
+    user_id = authenticate_user(image_data)
+
+    if user_id is None:
+        raise HTTPException(status_code=401, detail="인증 실패: 사용자 없음")
+
+    return {"user_id": user_id}
 
 
 @router.get("/users/{user_id}")
 def get_user_info(user_id: str):
     """회원 정보 조회 엔드포인트"""
-    pass
+    user_info = get_user(user_id)
+    if user_info is None:
+        raise HTTPException(status_code=404, detail="User not found")  
+    return user_info
 
 
 @router.delete("/users/{user_id}")
 def delete_user_info(user_id: str):
     """회원 삭제 엔드포인트"""
-    pass
+    result = delete_user(user_id)
+    if not result:
+        raise
+    HTTPException(status_code=404, detail="사용자가 존재하지 않습니다.")
+    return {"message": "사용자가 성공적으로 삭제되었습니다."}
diff --git a/app/face/face_db.py b/app/face/face_db.py
index 380ae3a..f3e27b5 100644
--- a/app/face/face_db.py
+++ b/app/face/face_db.py
@@ -1,16 +1,27 @@
+import json
+import os
+from datetime import datetime
 DB_PATH = "face_db.json"
 
 
 def save_user(user_id, embedding):
     """사용자 등록"""
-    pass
+    db = load_db()
+    db[user_id] = {"embedding": embedding, "registered_at": str(datetime.now())}
+    with open(DB_PATH, "w") as f:
+        json.dump(db, f)
 
 
 def load_db():
     """데이터베이스 로드"""
-    pass
+    if not os.path.exists(DB_PATH):
+        return {}
+    with open(DB_PATH, "r") as f:
+        return json.load(f)
+    
 
 
 def save_db(db):
     """데이터베이스 저장"""
-    pass
+    with open(DB_PATH, "w") as f:
+        json.dump(db, f)
diff --git a/app/face/face_embedding.py b/app/face/face_embedding.py
index 3acfb0c..05d770d 100644
--- a/app/face/face_embedding.py
+++ b/app/face/face_embedding.py
@@ -1,8 +1,13 @@
-def extract_embedding(image):
-    """이미지에서 임베딩 추출"""
-    pass
+import numpy as np
+from typing import Union
+from deepface import DeepFace
 
+def extract_embedding(img_path: Union[str, np.ndarray]) -> list:
+    """이미지에서 임베딩 추출"""
+    embedding = DeepFace.represent(img_path)[0]["embedding"]
+    return embedding
 
-def verify_embedding(embedding1, embedding2):
+def verify_embedding(embedding1: list, embedding2: list) -> bool:
     """두 임베딩이 같은 사람인지 검증"""
-    pass
+    is_same_person = DeepFace.verify(embedding1, embedding2)["verified"]
+    return is_same_person
diff --git a/app/services/user_service.py b/app/services/user_service.py
index 410b807..a0be8f2 100644
--- a/app/services/user_service.py
+++ b/app/services/user_service.py
@@ -1,18 +1,51 @@
+from datetime import datetime
+
+import cv2
+import numpy as np
+
+from app.face.face_db import load_db, save_db, save_user
+from app.face.face_embedding import extract_embedding, verify_embedding
+
 def register_user(user_id: str, image_bytes: bytes) -> dict:
     """이미지와 ID로 회원 등록"""
-    pass
+    image_np = np.frombuffer(image_bytes, dtype=np.uint8)
+    image = cv2.imdecode(image_np, cv2.IMREAD_COLOR)
+    embedding = extract_embedding(image)
+    save_user(user_id, embedding)
+    return {"user_id": user_id, "registered_at": str(datetime.now())}
 
 
 def authenticate_user(image_bytes: bytes):
     """이미지로 회원 인증"""
-    pass
+    image_np = np.frombuffer(image_bytes, dtype=np.uint8)
+    image = cv2.imdecode(image_np, cv2.IMREAD_COLOR)
+    db = load_db()
+
+    embedding_to_check = extract_embedding(image)
+
+    for user_id, data in db.items():
+        if verify_embedding(data["embedding"], embedding_to_check):
+            return user_id
+
+    return None
 
 
 def get_user(user_id):
     """user_id로 회원 정보 조회"""
-    pass
+    db = load_db()
+    user_data = db.get(user_id)
+
+    if user_data:
+        return {"user_id": user_id, "registered_at": user_data["registered_at"]}
+    else:
+        return None
 
 
 def delete_user(user_id):
     """user_id로 회원 삭제"""
-    pass
+    db = load_db()
+    if user_id in db:
+        del db[user_id]
+        save_db(db)
+        return True
+    return False
diff --git a/tests/conftest.py b/tests/conftest.py
index e69de29..fcfb780 100644
--- a/tests/conftest.py
+++ b/tests/conftest.py
@@ -0,0 +1,22 @@
+import pytest
+from fastapi.testclient import TestClient
+
+from app.face.face_db import save_user
+from app.face.face_embedding import extract_embedding
+from app.main import app
+
+
+@pytest.fixture(scope="module")
+def client():
+    with TestClient(app) as c:
+        yield c
+
+
+@pytest.fixture(scope="module")
+def setup_user_db():
+    image_paths = ["images/Aaron_Peirsol/Aaron_Peirsol_0001.jpg"]
+    user_ids = ["aaron_peirsol"]
+    for image_path, user_id in zip(image_paths, user_ids):
+        embedding = extract_embedding(image_path)
+        save_user(user_id, embedding)
+    yield
\ No newline at end of file
diff --git a/tests/test_api_users.py b/tests/test_api_users.py
index e69de29..b9ca6ce 100644
--- a/tests/test_api_users.py
+++ b/tests/test_api_users.py
@@ -0,0 +1,51 @@
+def test_register_user_api(client):
+    image_path = "images/Aaron_Peirsol/Aaron_Peirsol_0001.jpg"
+    user_id = "aaron_peirsol"
+
+    with open(image_path, "rb") as img_file:
+        response = client.post(
+            "/users/register",
+            data={"user_id": user_id},
+            files={"image": ("user1.jpg", img_file, "image/jpeg")},
+        )
+
+    assert response.status_code == 200
+    data = response.json()
+    assert data["user_id"] == user_id
+    assert data["registered_at"] is not None
+
+
+def test_authenticate_user_api(client, setup_user_db):
+    image_path = "images/Aaron_Peirsol/Aaron_Peirsol_0001.jpg"
+
+    with open(image_path, "rb") as img_file:
+        response = client.post(
+            "/users/authenticate",
+            files={"image": ("user1.jpg", img_file, "image/jpeg")},
+        )
+
+    assert response.status_code == 200
+    data = response.json()
+    assert data["user_id"] == "aaron_peirsol"
+
+
+def test_get_registered_user_api(client, setup_user_db):
+    user_id = "aaron_peirsol"
+
+    response = client.get(f"/users/{user_id}")
+
+    assert response.status_code == 200
+    data = response.json()
+    assert data["user_id"] == user_id
+    assert "registered_at" in data
+
+
+def test_delete_registered_user_api(client, setup_user_db):
+    user_id = "aaron_peirsol"
+
+    response = client.delete(f"/users/{user_id}")
+
+    assert response.status_code == 200
+
+    response = client.get(f"/users/{user_id}")
+    assert response.status_code == 404
\ No newline at end of file
diff --git a/tests/test_face.py b/tests/test_face.py
index e69de29..bcd5971 100644
--- a/tests/test_face.py
+++ b/tests/test_face.py
@@ -0,0 +1,32 @@
+import pytest
+
+from app.face.face_embedding import extract_embedding, verify_embedding
+
+
+def test_extract_embedding():
+    image_path = "images/Aaron_Peirsol/Aaron_Peirsol_0001.jpg"
+
+    embedding = extract_embedding(image_path)
+
+    assert embedding is not None
+    assert len(embedding) > 0
+
+
+def test_no_face_exception():
+    image_path = "tests/images/no_face.jpg"
+
+    with pytest.raises(ValueError):
+        extract_embedding(image_path)
+
+
+def test_verify_embedding():
+    image_path1 = "images/Aaron_Peirsol/Aaron_Peirsol_0001.jpg"
+    image_path2 = "images/Aaron_Peirsol/Aaron_Peirsol_0002.jpg"
+    image_path3 = "images/Olivia_Newton-John/Olivia_Newton-John_0001.jpg"
+
+    embedding1 = extract_embedding(image_path1)
+    embedding2 = extract_embedding(image_path2)
+    embedding3 = extract_embedding(image_path3)
+
+    assert verify_embedding(embedding1, embedding2)
+    assert not verify_embedding(embedding1, embedding3)
\ No newline at end of file
diff --git a/tests/test_service_users.py b/tests/test_service_users.py
index e69de29..518955b 100644
--- a/tests/test_service_users.py
+++ b/tests/test_service_users.py
@@ -0,0 +1,66 @@
+from app.services.user_service import (
+    authenticate_user,
+    delete_user,
+    get_user,
+    register_user,
+)
+
+
+def test_register_user():
+    image_path = "images/Aaron_Peirsol/Aaron_Peirsol_0001.jpg"
+    user_id = "aaron_peirsol"
+
+    with open(image_path, "rb") as f:
+        image_data = f.read()
+        result = register_user(user_id, image_data)
+
+    assert result["user_id"] == "aaron_peirsol"
+    assert result["registered_at"] is not None
+
+
+def test_authenticate_registered_user(setup_user_db):
+    image_path = "images/Aaron_Peirsol/Aaron_Peirsol_0001.jpg"
+
+    with open(image_path, "rb") as f:
+        image_data = f.read()
+        user_id = authenticate_user(image_data)
+
+    assert user_id == "aaron_peirsol"
+
+
+def test_authenticate_unregistered_user(setup_user_db):
+    image_path = "images/Natasha_McElhone/Natasha_McElhone_0001.jpg"
+    with open(image_path, "rb") as f:
+        image_data = f.read()
+
+    user_id = authenticate_user(image_data)
+
+    assert user_id is None
+
+
+def test_get_registered_user(setup_user_db):
+    user_id = "aaron_peirsol"
+
+    user_info = get_user(user_id)
+
+    assert user_info["user_id"] == user_id
+    assert "registered_at" in user_info
+
+
+def test_delete_registered_user(setup_user_db):
+    user_id = "aaron_peirsol"
+
+    result = delete_user(user_id)
+
+    assert result is True
+
+    user_info = get_user(user_id)
+    assert user_info is None
+
+
+def test_get_unregistered_user(setup_user_db):
+    user_id = "userA"
+
+    user_info = get_user(user_id)
+
+    assert user_info is None
\ No newline at end of file