var captchapng = require('captchapng');app.get('/sign/captcha.png', function(req, res) {var captchaNumber  = parseInt(Math.random() * 9000 + 1000)req.session.captcha = captchaNumbervar p = new captchapng(80,20, captchaNumber); // width,height,numeric captchap.color(0, 0, 0, 0); // First color: background (red, green, blue, alpha)p.color(80, 80, 80, 255); // Second color: paint (red, green, blue, alpha)var img = p.getBase64();var imgbase64 = new Buffer(img,'base64');res.writeHead(200, {'Content-Type': 'image/png'});res.end(imgbase64);})

$ npm install captchaUsage (for Express 4)'use strict'const express = require('express')const session = require('express-session')const bodyParser = require('body-parser')const captchaUrl = '/captcha.jpg'const captchaId = 'captcha'const captchaFieldName = 'captcha'const captcha = require('./captcha').create({ cookie: captchaId })const app = express()app.use(session({secret: 'keyboard cat',resave: false,saveUninitialized: true,}))app.use(bodyParser.urlencoded({ extended: false }))app.get(captchaUrl, captcha.image())app.get('/', (req, res) => {res.type('html')res.end(`<img src="${ captchaUrl }"/><form action="/login" method="post"><input type="text" name="${ captchaFieldName }"/><input type="submit"/></form>`)})app.post('/login', (req, res) => {res.type('html')res.end(`<p>CAPTCHA VALID: ${ captcha.check(req, req.body[captchaFieldName]) }</p>`)})app.listen(8080, () => {console.log('server started')})