This JavaScript code will help you convert any web URL into a PNG image from the command line. The script renders the page using Webkit, the same engine that’s used inside Google Chrome and Apple Safari browser. See demo at screenshot.guru.

var system = require('system');

// Web Address (URL) of the page to capture
var url = system.args[1];

// File name of the captured image
var file = system.args[2] + '.png';

var page = require('webpage').create();

// Browser size - height and width in pixels
// Change the viewport to 480x320 to emulate the iPhone
page.viewportSize = { width: 1200, height: 800 };

// Set the User Agent String
// You can change it to iPad or Android for mobile screenshots
page.settings.userAgent =
  'Mozilla/5.0 (Windows NT 6.1) AppleWebKit/536.5 (KHTML, like Gecko) Chrome/19.0.1084.56 Safari/536.5';

// Render the screenshot image
page.open(url, function (status) {
  if (status !== 'success') {
    console.log('Could not open web page : ' + url);
    phantom.exit();
  } else {
    window.setTimeout(function () {
      page.render(file);
      console.log('Download the screenshot : ' + file);
      phantom.exit();
    }, 1000);
  }
});