Data + duplicate Images upload on nodejs!

I'm starting now with NodeJS, and I'm testing an example that saves data along with an image upload.

It is working, but the image is duplicated.

I wanted to know where the error is, and why:

var express = require('express');
var app = express();
var fs = require("fs");
var bodyParser = require('body-parser');
var multer  = require('multer');


app.use(express.static('public'));
app.use(bodyParser.urlencoded({ extended: false }));

app.use(multer({dest:'tmp'}).single('file'));


app.get('/', function (req, res) {
   res.sendFile( __dirname + "/" + "index.html" );
})

app.post('/process_post', function (req, res) {
    console.log(req.file.originalname);
    console.log(req.file.path);
    console.log(req.file.mimetype);
    console.log('-----------');
    console.log(req.file);


   var file = __dirname + "/tmp/" + req.file.filename + '.jpg';

   fs.readFile(req.file.path, function (err, data) {
      fs.writeFile(file, data, function (err) {
         if( err ){
            console.log( err );
            }else{
               response = {
                  message:'Arquivo enviado com sucesso!',
                  filename:req.file.filename + '.jpg',
                  first_name:req.body.first_name,
                  last_name:req.body.last_name
               };
            }
         console.log( response );
         res.end(JSON.stringify( response ));
      });
   });
})

var server = app.listen(8081, function () {
   var port = server.address().port
   console.log("Servidor iniciado em http://localhost:%s", port)

})

HTML:

  <form action = "http://127.0.0.1:8081/process_post" method = "POST" enctype = "multipart/form-data">
     First Name: <input type = "text" name = "first_name">  <br>
     Last Name: <input type = "text" name = "last_name"> <br>
     Foto: <input type="file" name="file" size="50" /> <br>
     <input type = "submit" value = "Submit">
  </form>

CONSOLE.LOG

C_OURO.png
tmpac6310c0d101cb280f1f9bbfe1bfb0
image/png
-----------
{ fieldname: 'file',
  originalname: 'C_OURO.png',
  encoding: '7bit',
  mimetype: 'image/png',
  destination: 'tmp',
  filename: '19ac6310c0d101cb280f1f9bbfe1bfb0',
  path: 'tmp\19ac6310c0d101cb280f1f9bbfe1bfb0',
  size: 5555562 }
{ message: 'Arquivo enviado com sucesso!',
  filename: '19ac6310c0d101cb280f1f9bbfe1bfb0.jpg',
  first_name: 'Nome',
  last_name: 'Sobrenome' }

Thank you!