express.js how show image?

I have images in /public folder and I want to show them..simply like this: <img src="a.jpg">

My app.js code

var express = require('express')
  , app = express()
  , http = require('http')
  , server = http.createServer(app)
  , io = require('socket.io').listen(server);

server.listen(8080);    
app.use('/public', express.static(__dirname + "/public"));

If I open it in localhost this error is still showing

NetworkError: 404 Not Found - http://localhost:8080/public/a.jpg"