diff --git a/app/api/users.py b/app/api/users.py
index 043dd98..6691f3d 100644
--- a/app/api/users.py
+++ b/app/api/users.py
@@ -1,5 +1,6 @@
-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 *
 
 router = APIRouter()
 
@@ -7,22 +8,43 @@
 @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='사용자가 존재하지 않습니다.')
+
+    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.'}
\ No newline at end of file
diff --git a/app/face/face_db.py b/app/face/face_db.py
index 380ae3a..eaf2b39 100644
--- a/app/face/face_db.py
+++ b/app/face/face_db.py
@@ -1,16 +1,25 @@
+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)
\ No newline at end of file
diff --git a/app/services/user_service.py b/app/services/user_service.py
index 410b807..fa1ce6a 100644
--- a/app/services/user_service.py
+++ b/app/services/user_service.py
@@ -1,18 +1,49 @@
+import cv2
+import numpy as np
+from datetime import datetime
+
+from app.face.face_embedding import *
+from app.face.face_db import *
+
 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
\ No newline at end of file
diff --git a/tests/conftest.py b/tests/conftest.py
index e69de29..48d7a1e 100644
--- a/tests/conftest.py
+++ b/tests/conftest.py
@@ -0,0 +1,20 @@
+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
diff --git a/tests/test_api_users.py b/tests/test_api_users.py
index e69de29..c9ddd06 100644
--- a/tests/test_api_users.py
+++ b/tests/test_api_users.py
@@ -0,0 +1,48 @@
+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..41b3148 100644
--- a/tests/test_face.py
+++ b/tests/test_face.py
@@ -0,0 +1,66 @@
+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..93c5a13 100644
--- a/tests/test_service_users.py
+++ b/tests/test_service_users.py
@@ -0,0 +1,54 @@
+from app.services.user_service import *
+
+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_id = get_user(user_id)
+    assert user_id is None
+
+def test_non_authenticate_user(setup_user_db):
+    user_id = 'non_existent_user'
+
+    user = get_user(user_id) 
+
+    assert user is None 
\ No newline at end of file