How to use resemble.js?

How to use resemble.js?

I was looking through resemble.js's demos and tried to use it with the
following code:
resemble("https://www.google.com/images/srpr/logo4w.png").compareTo("https://www.google.com/images/srpr/logo4w.png").onComplete(function(data){
if(data.misMatchPercentage == 0){
alert("hello");
}
});
For some reason it never alerts hello. What could I be doing wrong? Do the
arguments have to be canvas or image objects?