This is a simple demonstration how to download remote images (assuming the image server supports CORS) in a Web Worker and draw them on a canvas in the main UI browser thread.
It uses XMLHttpRequest2 to fetch image as a
blob and then pases the URL created with window.URL.createObjectURL to the main UI thread.
Beware that this code is not optimized in any way, e.g. as far as memory consumption is concerned. In the current form it constantly creates function objects, etc.
This is free and unencumbered software released into the public domain. For more information, please refer to http://unlicense.org/