I was also encountered with such a problem where I needed static image based charts on server side using PHP. I found a way to achieve this using PhantomJS and Google Chart's javascript api. Following is an example of how to do this...
var webPage = require('webpage');
var page = webPage.create();
page.includeJs("https://www.gstatic.com/charts/loader.js", function() {
var expectedContent = '' +
'' +
' '+
''+
''+
''+
''+
'';
var expectedLocation = 'http://www.phantomjs.org/';
page.setContent(expectedContent, expectedLocation);
window.setTimeout(function () {
page.render("mypng.png");
phantom.exit();
}, 1000); // Change timeout as required to allow sufficient time
});
After that you need to run this javascript file within your PHP:-
exec(ROOT_DIRECTORY . "\phantomjs.exe processImageData.js ", $output);