With PhantomJs you can capture website and save by png. e.g.: call: phantomjs capture.js url width height outputFileName

Phantomjs capture website screen

#! /usr/bin/phantomjs

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

if(args[1]==''){
	console.log('Url parameter is missign!')
	console.log('Important to call this file for four parameters.');
	console.log('phantomjs url w h output file name');
	phantom.exit();
}

if(args[2]==''){
	console.log('Width parameter is missign!')
	console.log('Important to call this file for four parameters.');
	console.log('phantomjs url w h output file name');
	phantom.exit();
}

if(args[3]==''){
	console.log('Height parameter is missign!')
	console.log('Important to call this file for four parameters.');
	console.log('phantomjs url w h output file name');
	phantom.exit();
}

if(args[4]==''){
	console.log('Output parameter is missign!')
	console.log('Important to call this file for four parameters.');
	console.log('phantomjs url w h output file name');
	phantom.exit();
}

console.log(args[1], args[2], args[3], args[4]);
var savedImagePath = "/path/to/your/tmp/folder/" + args[4]

page.viewportSize = { width: args[2], height: args[3] };
page.open(args[1], function(status) {
	if (status !== 'success') {
        phantom.exit();
    } else {
        window.setTimeout(function () {
            page.render(savedImagePath);
			console.log(savedImagePath);
            phantom.exit();
        }, 1000); // Change timeout as required to allow sufficient time 
    }
});