CreateImage without CORS => tainted canvas

[forresto]

In the browser, image.crossOrigin = "Anonymous" needs to be set before the image is loaded. Otherwise, drawing the image to a canvas makes it impossible to get the pixels out of that canvas (context.drawImage works, but later getImageData won't).

You can't set it for all images, b/c non-CORS-served images will crash on load. I guess we could catch that and retry without crossOrigin. Or retry with our own CORS proxy.

This isn't an issue on Node.

[forresto]

UrlToCanvas graph should be smart enough to cache / proxy non-CORS images.