The following script shows how to highlight a particular element on an HTML page using PhantomJS before taking a screenshot.

highlight-and-rasterize.js

var webpage = require('webpage');
var page = webpage.create();
page.viewportSize = { width: 1600, height: 900 };

page.open('http://sangupta.com/poetry/best-of-luck.html', function() {
  // execute the selector
  var ev = page.evaluate(function(sel) {
    var ele = document.querySelector(sel);
	  if(ele) {
      ele.style.border = "2px solid red";
      return true;
	  }
    console.log('ele not found');
    return false;
  }, 'body > div.container-fluid.full-height > div > div.col-sm-3.col-md-2.sidebar > div > div > div:nth-child(3)');
  
  // log the result
  console.log('result is: ' + ev);
  
  // take the snapshot
  page.render('myscreenshot.png');
  
  // exit phantomjs
  phantom.exit();
});