A Facial Recognition utility in a dozen of LOC

A Facial Recognition utility in a dozen of python LOC (Lines Of Code)

CV (Computer Vision)

I have been soak myself in open sourced libraries, such as OpenCV. I gradually came to discern concepts such as Machine Learning , Deep Learning are not academic standing water. As a matter of fact, those elusive topics and certain pragmatic use cases could coalesce in a amount of interesting products. For instance, in past couple of months, there were a hype of guess-ages-by-photo, below screenshot depicts such.

What a seductive one! Initially been attracted by such funky features, after second thoughts, I found at the heart of it is two cohesive parts, the first one is how to locate human faces from background and whole picture, consequently to have a ballpark age guess for the recognized the faces. You may guess how difficult to codify a program to implement the 1st feature. Actually no need chunks of code, at here purely a dozen of lines of code are necessitated (actually only 10 lines of code, excluding space line and comments). I’d like to piggyback on such tiny utility to elaborate advanced topics of Computer Visions.

Faces recognition

Actually face recognition is not new to us, this feature prevailing in so-called auto focus in DC (Digital Camera) and many main stream smart phone built-in cameras. Just like below photo. You can get a sense of how commonplace of face recognition , which is becoming a widely used technology around us.

Theoretically speaking, face recognition is also called face detection, it’s a type of technology/program to electronically identify human frontal faces in digital images, such as photos, camera or surveillance. Further more, face detection is kind of objects detection in computer vision area. Which will locate object (e.g. human face) and get the size.

My ‘10 LOC program’

First of all, let’s have some visual and concrete feeling of this program, below screenshot is the source code.

The whole program source code can be found at this github repository https://github.com/CloudsDocker/pyFacialRecognition . Please feel free to fork , check it out and have a try. I’ll walk through this program one line by one line at this blog.

“You serious? This is all the problem, just aforementioned 10 lines?” Let’s first take a look at the actual run output.

Here is the origional image

Below is the result of execution of this tiny utility

Please be advised the red rectangle around faces.

Souce Code


First of first, as you know, this program is composed by python,therefore, make sure you work station or laptop equiped with python, vesrion is irrelavant for this program.

In addition, this utility is built upon OpenCV (http://opencv.org/downloads.html), therefore please install this component as well. Just as its name suggested, it is an open source framework focus on computer vision related deep learning, surfaced decades ago. This is one Intel lab built by Rusian, which is a very active community.

Particulary, if you are Mac users, it’s recommended to use brew to setup OpenCV. Below is sample commands(The 1st line of following command may raise some errors, in that case please contact me via the link at the rear of this blog):

brew tap homebrew/science
brew install opencv

Upon completion of preceding scripts, you can execute following scripts to verify whether it’s installed success or not, e.g. it means all fine if no exception/errors raised

>>> import cv2

Souce Code Dissection

Let’s dissect file recognizeFace_loose_en.py as one example

import cv2,sys
  • To import library of OpenCV and python built-in system library, which is used to parse input arguments.
  • To read the 1st argument, which to be the file name of the image to be parsed, e.g. test.jpg
  • To load HAAR Casscade Classifier, the human face recognition cascade categorizer which shipped with OpenCV. Which will do the actual computation, logic to recognize and size human faces from any given images.

Expansion of computer vision knowledge

We stop here not reading further code, avoiding perplex you, I’ll walk through certain CV topics pertaining to this blog. As for more deep concepts, please feel free to contact me or goole by yourself.


In arena of computer vision and machine learning, a variaty of classifiers been and being built, to assemle special domain knowledge to recognize corresponding objects. For example, there are particular classifier to recognize cars, there are plane classifier, and classifiers to recognize smile, eyes, etc. For our case, we need a specific classifier help us to detect and locate human faces.

Conceps of objects recognize

Generally speaking,, to recognize one object (such as human faces) means finding and identifying objects in an image or video sequence. However, it’s neccessitate tons of sample/specimen to train machine to learn, for instance, it’s likely thousands of hundreds of digital images/video will be prepared as learning material, while all of specimen should be categorized to two mutax type, positive or negative. e.g. phots containss human face and ones without human face. When machine read one photo, it was told this is either a positive one or negative one, then machine could gradually analysys and induce some common facets and persist to files for future usages, e.g. when given a new photo, the machine can classify it whether it’s a positive or negative. That’s why it’s called classifier.


Your feeling is right, just as it’s name suggrested, cascade implies propagating something. In this case, it’s specifically means Cascade classifier. Intuitively the next question is why cascade is required? Let me try to articulate the underlying logic, as you know, at the heart of digital images, which is the raw material of computer vision, are pixel。For one CV process, it need to scan each pixel per pixel, while in contemporary world, size of image tend to incresing more than we expected, e.g. normall one photo taken by smart phone tend to contains millions of pixels. At the meanwhile, to fine tune and get a more accuate result of one object recognition, it tend to lots of classifiers to work from different point of views of the underlying photo. Therefore these two factors interwhirled together, the final number would be astronomical. Therefore, one innovative solution is cascade, in a nutshell, all classifiers will be splited to multiple layers, one photo will be examined by classifiers on 1st layer at the very begining, if failed, the whole CV can retain negative immediately, with fewest efforts and time cost, while majority of other classifiers won’t be executed in actual. This should significantely accelerate the whole process of CV. This is similar to FF(Fail Fast) in other areas,severed for sake of running efficiency.

  • To create one OpenCV image object by loading the input digital file via OpenCV
  • Firstly, convert the digital colorful image to grayscale one, which easy the task to scan and analyse the image. Actually this is quite common in image analys area. e.g. this could eliminate those noisy pixel from the picture.
foundFaces=faceClassifier.detectMultiScale(cvtImage,scaleFactor=1.3,minNeighbors=9,minSize=(50,50),flags = cv2.cv.CV_HAAR_SCALE_IMAGE)
  • Call method detectMultiScale to recongnize object, i.e. human face in this case. The parameters overview as below:
  • scaleFactor: For a photo, particualy from selpie, some faces are shows bigger than rest of others, due to the distance between each faces and lens. Therefore this parameter is used to config the factor, please be advised this double should greater than 1.0
  • minNeighbors: Because it need to gradually scan the photo by a certain window, i.e. a rectangle. So this parameter is telling how many other object in the vacinity to be detected, before making final decision that it’s positive or negative.
  • minSize:For aforementioend window, this parameter is setting the size of this rectangle.
print(" Found {} human faces in this image".format(len(foundFaces)))
  • To print how many faces detected, be reminded returned value is a list, each item is the actual position of every faces. Therefore, using len to print total number of ojects found.
for (x,y,w,h) in foundFaces:
  • Traverese all faces detected, please be noted returning object is consist of 4 parts, i.e. the horizontal and vertial position, width and height.
  • Consequently to draw a rectangle by an off-the-shelf method from OpenCV. Be advised (0,0,255) represents color of the rectangel. It use R/G/B mode, e.g. black is (0,0,0),white is (255,255,255),etc. Well versed web programmer should be familiar with it.
cv2.imshow('Detected human faces highlighted. Press any key to exit. ', objImage)
  • To display this image via opencv provided method imshow, together with the rectangles we draw previously
  • The last one is one user hint, remind you can quit the applicaiton by press any key on the image display window

In summary

We’ve skimmed source codes and pertaining knowledge. This is just scratched the surface of this framework, hope this can open the door to more advanced topics and insights, such as hack of CAPTCHA, newly open sourced project form Yahoo, NSFW, Not Suitable for Work (NSFW),to detect images with pornagraphy, etc.

Finally,please be reminded all related source are open sourced at github repository https://github.com/CloudsDocker/pyFacialRecognition ,please fork and sync to your local disk, check it out and paly it.

git clone https://github.com/CloudsDocker/pyFacialRecognition.git
cd pyFacialRecognition

You can access my blog. Any comments/suggestions, feel free to contact me.

Contact me:

  • phray.zhang@gmail.com (email,whatsapp, linkedin)
  • helloworld_2000 (wechat)
  • weibo: cloudsdocker
  • github
  • jianshu
  • wechat:vibex



Back to Top ↑


Az Cli

To run commands in VMs in Azure

Cheap and flexible computing

whether it seems possible or not - go for it Cheaper X 2 to EC2, to use Fargate Spot With Fargate Spot you can run interruption tolerant Amazon ECS t...


Summary As a Java developer, it’s important to know how to find out which port number your Spring service is running on. This information is useful when you ...

Elk Search Tips

message:/'Invoking SP with quoteContext*werqewr-1234asdf-sdf23-9d83-asdf23*'/

what is StrictHostKeyChecking in ssh

What’s and how to avoid error of the authenticity of host ‘xxx’ can’t be established You can suppress the “The authenticity of host ‘’ can’t be established” ...

Spring Cloud Master Piece 9

What’s spring cloud config Spring Cloud Config is a distributed configuration server that provides a centralized location to manage external properties for a...

Spring Cloud Master Piece 6

Sample me build a micro service payment system with spring cloud Here’s an example of building a microservice payment system using Spring Cloud:

Spring Cloud Master Piece 2

what’s usage of bootstrap yml In a Spring Boot application, the bootstrap.yml (or bootstrap.properties) file is used for configuring the application’s enviro...

Spring Cloud Master Piece 1

what’s API gateway An API Gateway is a key component in microservices architecture that acts as a single entry point for client requests to a microservices-b...

How To Config JFR Java Flight Control

“Climb the mountains and get their good tidings. Nature’s peace will flow into you as sunshine flows into trees. The winds will blow their own freshness i...

Google マップ内の写真のコメントが表示されない

紹介 私は、私のOppo Androidスマートフォンのアプリ「Googleマップ」で奇妙な問題が発生していることに気づきました。Googleマップで特定の場所(例えば「中央公園」)を検索すると、通常、このアプリは公園の写真やコメントリストを表示するはずです。例えば、誰かが公園の芝生や川の写真を投稿し、便利な場所...

Back to Top ↑


Minium Workable Mvp Vimrc

”—————————————————————- “ 4. User interface “—————————————————————- “ Set X lines to the cursor when moving vertically set scrolloff=0

Linux Tips

Remember, some things have to end for better things to begin.

Back to Top ↑


How to user fire extinguisher

Summary As you know, staff and your safety is paramount. So what if emergency take place, such as fire in office, how to help yourself and your colleagues by...

Deep dive into Kubernetes Client API

Summary To talk to K8s for getting data, there are few approaches. While K8s’ official Java library is the most widely used one. This blog will look into thi...

Whitelabel Error Page

Summary Whitelabel Error Page is the default error page in Spring Boot web app. It provide a more user-friently error page whenever there are any issues when...

Debts in a nutshell

A debt security represents a debt owed by the issuer to an investor. Here, the investor acts as a lender to the issuer which may be a government, organisatio...

Back to Top ↑


Debug Stuck IntelliJ

What happened to a debug job hanging in IntelliJ (IDEAS) IDE? You may find when you try to debug a class in Intellij but it stuck there and never proceed, e....

Awesome Kotlin

Difference with Scala Kotlin takes the best of Java and Scala, the response times are similar as working with Java natively, which is a considerable advantag...



Mock in kotlin

Argument Matching & Answers For example, you have mocked DOC with call(arg: Int): Intfunction. You want to return 1 if argument is greater than 5 and -1 ...

Mock in kotlin

Argument Matching & Answers For example, you have mocked DOC with call(arg: Int): Intfunction. You want to return 1 if argument is greater than 5 and -1 ...


Linux Curl command


The concept of join points as matched by pointcut expressions is central to AOP, and Spring uses the AspectJ pointcut expression language by default.

Micrometer notes

As a general rule it should be possible to use the name as a pivot. Dimensions allow a particular named metric to be sliced to drill down and reason about th...

Awesome SSL certificates and HTTPS

What’s TLS TLS (Transport Layer Security) and its predecessor, SSL (Secure Sockets Layer), are security protocols designed to secure the communication betwee...

JVM warm up by Escape Analysis

Why JVM need warm up I don’t know how and why you get to this blog. But I know the key words in your mind are “warm” for JVM. As the name “warm up” suggested...

Java Concurrent

This blog is about noteworthy pivot points about Java Concurrent Framework Back to Java old days there were wait()/notify() which is error prone, while fr...

Back to Top ↑


Conversations with God

Feelings is the language of the soul. If you want to know what’s true for you about something, look to how your’re feeling about.

Kafka In Spring

Enable Kafka listener annotated endpoints that are created under the covers by a AbstractListenerContainerFactory. To be used on Configuration classes as fol...


FX Spot is not covered by the regulation, as it is not considered to be a financial instrument by ESMA, the European Union (EU) regulator. As FX is considere...

Foreign Exchange

currency pairs Direct ccy: means USD is part of currency pair Cross ccy: means ccy wihtout USD, so except NDF, the deal will be split to legs, both with...

Back to Top ↑



A new type of Juice Put simply, Guice alleviates the need for factories and the use of new in your Java code. Think of Guice’s @Inject as the new new. You wi...


Key points All YAML files (regardless of their association with Ansible or not) can optionally begin with — and end with …. This is part of the YAML format a...

Sudo in a Nutshell

Sudo in a Nutshell Sudo (su “do”) allows a system administrator to give certain users (or groups of users) the ability to run some (or all) commands as root...


ZK Motto the motto “ZooKeeper: Because Coordinating Distributed Systems is a Zoo.”


Acceptance testing vs unit test It’s sometimes said that unit tests ensure you build the thing right, whereas acceptance tests ensure you build the right thi...

akka framework of scala

philosophy The actor model adopts the philosophy that everything is an actor. This is similar to the everything is an object philosophy used by some object-o...

Apache Camel

Camel’s message model In Camel, there are two abstractions for modeling messages, both of which we’ll cover in this section. org.apache.camel.Message—The ...


Exporting your beans to JMX The core class in Spring’s JMX framework is the MBeanExporter. This class is responsible for taking your Spring beans and registe...

Solace MQ

Solace PubSub+ It is a message broker that lets you establish event-driven interactions between applications and microservices across hybrid cloud environmen...


App deployment, configuration management and orchestration - all from one system. Ansible is powerful IT automation that you can learn quickly.


Ansible: What Is It Good For? Ansible is often described as a configuration management tool, and is typically mentioned in the same breath as Chef, Puppet, a...


How Flexbox works — explained with big, colorful, animated gifs


KDB However kdb+ evaluates expressions right-to-left. There are no precedence rules. The reason commonly given for this behaviour is that it is a much simple...

Agile and SCRUM

Key concept In Scrum, a team is cross functional, meaning everyone is needed to take a feature from idea to implementation.


Release & Testing Strategy There are various methods for safely releasing changes to Production. Each team must select what is appropriate for their own ...

NodeJs Notes

commands to read files var lineReader = require(‘readline’).createInterface({ input: require(‘fs’).createReadStream(‘C:\dev\node\input\git_reset_files.tx...

CORS :Cross-Origin Resource Sharing

Cross-Origin Request Sharing - CORS (A.K.A. Cross-Domain AJAX request) is an issue that most web developers might encounter, according to Same-Origin-Policy,...


Why @Effects? In a simple ngrx/store project without ngrx/effects there is really no good place to put your async calls. Suppose a user clicks on a button or...

iOS programming

View A view is also a responder (UIView is a subclass of UIResponder). This means that a view is subject to user interactions, such as taps and swipes. Thus,...

Back to Top ↑


cloud computering

openshift vs openstack The shoft and direct answer is `OpenShift Origin can run on top of OpenStack. They are complementary projects that work well together....

cloud computering

Concepts Cloud computing is the on-demand demand delivery of compute database storage applications and other IT resources through a cloud services platform v...


whats @Effects You can almost think of your Effects as special kinds of reducer functions that are meant to be a place for you to put your async calls in suc...

reactive programing

The second advantage to a lazy subscription is that the observable doesn’t hold onto data by default. In the previous example, each event generated by the in...


The Docker project was responsible for popularizing container development in Linux systems. The original project defined a command and service (both named do...

promise vs observiable

The drawback of using Promises is that they’re unable to handle data sources that produce more than one value, like mouse movements or sequences of bytes in ...

JDK source

interface RandomAccess Marker interface used by List implementations to indicate that they support fast (generally constant time) random access. The primary ...


Secure FTP SFTP over FTP is the equivalant of HTTPS over HTTP, the security version

AWS Tips

After establishing a SSH session, you can install a default web server by executing sudo yum install httpd -y. To start the web server, type sudo service htt...


ORA-12899: Value Too Large for Column

Kindle notes

#《亿级流量网站架构核心技术》目录一览 TCP四层负载均衡 使用Hystrix实现隔离 基于Servlet3实现请求隔离 限流算法 令牌桶算法 漏桶算法 分布式限流 redis+lua实现 Nginx+Lua实现 使用sharding-jdbc分库分表 Disruptor+Redis...

Java Security Notes

Java Security well-behaved: programs should be prevent from consuming too much system resources

R Language

s<-read.csv("C:/Users/xxx/dev/R/IRS/SHH_SCHISHG.csv") # aggregate s2<-table(s$Original.CP) s3<-as.data.frame(s2) # extract by Frequency ordered s3...

SSH and Cryptography

SFTP versus FTPS SS: Secure Shell An increasing number of our customers are looking to move away from standard FTP for transferring data, so we are ofte...

Eclipse notes

How do I remove a plug-in? Run Help > About Eclipse > Installation Details, select the software you no longer want and click Uninstall. (On Macintosh i...


Maven philosophy “It is important to note that in the pom.xml file you specify the what and not the how. The pom.xml file can also serve as a documentatio...

Java New IO

Notes JDK 1.0 introduced rudimentary I/O facilities for accessing the file system (to create a directory, remove a file, or perform another task), accessi...


SOA SOA is a set of design principles for building a suite of interoperable, flexible and reusable services based architecture. top-down and bottom-up a...


This page is about key points about Algorithm


What is the difference between Serializable and Externalizable in Java? In earlier version of Java, reflection was very slow, and so serializaing large ob...


Concepts If you implement Comparable interface and override compareTo() method it must be consistent with equals() method i.e. for equal object by equals(...

Java Collections Misc

Difference between equals and deepEquals of Arrays in Java Arrays.equals() method does not compare recursively if an array contains another array on oth...

HashMap in JDK

Hashmap in JDK Some note worth points about hashmap Lookup process Step# 1: Quickly determine the bucket number in which this element may resid...

Java 8 Tips

This blog is listing key new features introduced in Java 8

Back to Top ↑


Java GC notes

verbose:gc verbose:gc prints right after each gc collection and prints details about each generation memory details. Here is blog on how to read verbose gc

Hash Code Misc

contract of hashCode : Whenever it is invoked on the same object more than once during an execution of a Java application, the hashCode method must consis...

Angulary Misc

Dependency Injection Angular doesn’t automatically know how you want to create instances of your services or the injector to create your service. You must co...

Java new features

JDK Versions JDK 1.5 in 2005 JDK 1.6 in 2006 JDK 1.7 in 2011 JDK 1.8 in 2014 Sun之前风光无限,但是在2010年1月27号被Oracle收购。 在被Oracle收购后对外承诺要回到每2年一个realse的节奏。但是20...

Simpler chronicle of CI(Continuous Integration) “乱弹系列”之持续集成工具

引言 有句话说有人的地方就有江湖,同样,有江湖的地方就有恩怨。在软件行业历史长河(虽然相对于其他行业来说,软件行业的历史实在太短了,但是确是充满了智慧的碰撞也是十分的精彩)中有一些恩怨情愁,分分合合的小故事,比如类似的有,从一套代码发展出来后面由于合同到期就分道扬镳,然后各自发展成独门产品的Sybase DB和微...

浅谈软件单元测试中的“断言” (assert),从石器时代进步到黄金时代。


Kubernetes 与 Docker Swarm的对比

Kubernetes 和Docker Swarm 可能是使用最广泛的工具,用于在集群环境中部署容器。但是这两个工具还是有很大的差别。

http methods

RFC origion http://www.w3.org/Protocols/rfc2616/rfc2616-sec9.html#sec9.1.2)


The stark difference among Spark and Storm. Although both are claimed to process the streaming data in real time. But Spark processes it as micro-batches; wh...



kibana, view layer of elasticsearch

What’s Kibana kibana is an open source data visualization plugin for Elasticsearch. It provides visualization capabilities on top of the content indexed on...

kibana, view layer of elasticsearch

What’s Kibana kibana is an open source data visualization plugin for Elasticsearch. It provides visualization capabilities on top of the content indexed on...


UI HTML5, AngularJS, BootStrap, REST API, JSON Backend Hadoop core (HDFS), Hive, HBase, MapReduce, Oozie, Pig, Solr

Data Structure

Binary Tree A binary tree is a tree in which no node can have more than two children. A property of a binary tree that is sometimes important is that th...


Differences between not in, not exists , and left join with null

Github page commands notes

404 error for customized domain (such as godday) 404 There is not a GitHub Pages site here. Go to github master branch for gitpages site, manually add CN...

RenMinBi International

RQFII RQFII stands for Renminbi Qualified Foreign Institutional Investor. RQFII was introduced in 2011 to allow qualified foreign institutional investors to ...

Load Balancing

Concepts LVS means Linux Virtual Server, which is one Linux built-in component.


(‘—–Unexpected error:’, <type ‘exceptions.TypeError’>) datetime.datetime.now()

Microservices vs. SOA

Microservice Services are organized around capabilities, e.g., user interface front-end, recommendation, logistics, billing, etc. Services are small in ...

Java Class Loader

Codecache The maximum size of the code cache is set via the -XX:ReservedCodeCacheSize=N flag (where N is the default just mentioned for the particular com...

Back to Top ↑