testLabelary.js

var fs = require('fs');
var request = require('request');

request.post({ body: "^xa^cfa,50^fo100,100^fdHello World^fs^xz", encoding: null, url: 'http://api.labelary.com/v1/printers/8dpmm/labels/4x6.75/0/' }, function(err, resp, body) {
    if (err) {
        return console.log(err);
    }

    console.log('headers', resp.headers);
    console.log('status', resp.statusCode);
    console.log('body', body);

    if (body.length < 1000) {
        console.log(new Buffer(body).toString());
    }

    fs.writeFile('./label.png', body, function(err) {
        if (err) {
            console.log(err);
        }
    });
});

console output:

headers { 'access-control-allow-origin': '*',
  'content-type': 'text/plain',
  date: 'Fri, 22 Apr 2016 16:48:42 GMT',
  'x-vcap-request-id': '5c702169-4c85-4a89-69e2-c4aa06429a70',
  'content-length': '38',
  connection: 'Close' }
status 415
body <Buffer 45 52 52 4f 52 3a 20 48 54 54 50 20 34 31 35 20 55 6e 73 75 70 70 6f 72 74 65 64 20 4d 65 64 69 61 20 54 79 70 65>
ERROR: HTTP 415 Unsupported Media Type