title: Generate image data from HTML Canvas element
body: <p>What is the best way to generate image data from the contents of an HTML canvas element?</p>
  
  <p>I'd like to create the image data such that it can be transmitted to a server (it's not necessary for the user to be able to directly save to a file). The image data should be in a common format such as PNG or JPEG. </p>
  
  <p>Solutions that work correctly in multiple browsers are preferred, but if every solution depends on the browser, recent versions of Firefox should be targeted.</p>