title: How to detect if an image generated via canvas is blank (transparent PNG)?
body: <p>I am working on an application in which an image is created/edited on a HTML5 canvas and then saved into a file-store/cloud. The problem is that of "saving efficiency". On save of a blank canvas, i.e. a totally transparent blank PNG is sent with <code>toDataURL()</code>. One way of detecting a blank PNG is by switching a boolean value upon click of any editing/drawing functionality and reseting that value upon clear-screen. </p>
  
  <p>However, such a method is not foolproof because a user may save the image after clicking a draw/edit function and yet not draw anything. Is there a more native approach to detect if the canvas returns a binary string that has changed since opening up on the browser? Or some other way to ensure that a blank transparent PNG is detected at client side?</p>