Perfect! I don't have any need to convert to png first - just thought I would have to. Even better to simply draw directly on the canvas and have it rendered.
The demo name on your demos page (https://clara.io/docs/tutorial-8_Demos.html) is misspelled though. I was sure I had searched that page for canvas. On your page it's: "External Cavas". Might save you a few forum posts to fix that. :)
Thanks for your help!