diff --git a/README.md b/README.md
index 619f207..493ec77 100644
--- a/README.md
+++ b/README.md
@@ -100,14 +100,21 @@ print("Race: ", demography["dominant_race"])
 
 **Face Detectors** - [`Demo`](https://youtu.be/GZ2p2hj2H5k)
 
-Face detection and face alignment are early stages of a modern face recognition pipeline. [OpenCV](https://sefiks.com/2020/02/23/face-alignment-for-face-recognition-in-python-within-opencv/), [SSD](https://sefiks.com/2020/08/25/deep-face-detection-with-opencv-in-python/), [Dlib](https://sefiks.com/2020/07/11/face-recognition-with-dlib-in-python/) and MTCNN methods are wrapped in deepface as a detector. You can pass a custom detector to functions in deepface interface. OpenCV is the default detector for the package.
+Face detection and alignment are early stages of a modern face recognition pipeline. [OpenCV haar cascade](https://sefiks.com/2020/02/23/face-alignment-for-face-recognition-in-python-within-opencv/), [SSD](https://sefiks.com/2020/08/25/deep-face-detection-with-opencv-in-python/), [Dlib](https://sefiks.com/2020/07/11/face-recognition-with-dlib-in-python/) and MTCNN methods are wrapped in deepface as a detector. You can optionally pass a custom detector to functions in deepface interface. OpenCV is the default detector if you won't pass a detector.
 
 ```python
 backends = ['opencv', 'ssd', 'dlib', 'mtcnn']
 for backend in backends:
-   detected_face = DeepFace.detectFace("img.jpg", detector_backend = backend) #detectors in face detection and alignment
-   obj = DeepFace.verify("img1.jpg", "img2.jpg", detector_backend = backend) #detectors in verification
-   df = DeepFace.find(img_path = "img.jpg", db_path = "my_db", detector_backend = backend) #detectors in face recognition
+   #face detection and alignment
+   detected_face = DeepFace.detectFace("img.jpg", detector_backend = backend)
+   
+   #face verification
+   obj = DeepFace.verify("img1.jpg", "img2.jpg", detector_backend = backend)
+   
+   #face recognition
+   df = DeepFace.find(img_path = "img.jpg", db_path = "my_db", detector_backend = backend)
+   
+   #facial analysis
    demography = DeepFace.analyze("img4.jpg", detector_backend = backend) #detectors in facial analysis
 ```
 
diff --git a/deepface/commons/functions.py b/deepface/commons/functions.py
index 8eca205..1b33b45 100644
--- a/deepface/commons/functions.py
+++ b/deepface/commons/functions.py
@@ -126,13 +126,6 @@ def load_image(img):
 	
 def detect_face(img, detector_backend = 'opencv', grayscale = False, enforce_detection = True):
 	
-	detectors = ['opencv', 'ssd', 'dlib', 'mtcnn']
-	
-	if detector_backend not in detectors:
-		raise ValueError("Valid backends are ", detectors," but you passed ", detector_backend)
-	
-	#---------------------------
-	
 	home = str(Path.home())
 	
 	if detector_backend == 'opencv':
@@ -302,6 +295,10 @@ def detect_face(img, detector_backend = 'opencv', grayscale = False, enforce_det
 			else:
 				raise ValueError("Face could not be detected. Please confirm that the picture is a face photo or consider to set enforce_detection param to False.")
 	
+	else:
+		detectors = ['opencv', 'ssd', 'dlib', 'mtcnn']
+		raise ValueError("Valid backends are ", detectors," but you passed ", detector_backend)
+	
 	return 0
 
 def alignment_procedure(img, left_eye, right_eye):