Hello DaveRo,
No canvas addons/plugins - though I'll be taking a look at the one you mentioned.
( Whilst I have concerns about the privacy/anonymity/persistent tracking capabilities of using HTML 5 Canvas, the actual technology and potential is of interest)
The problem (such as it is ) is entirely of my doing - I have followed Mozilla's own instructions about disabling Canvas, and am discovering the impact of that choice. Currently that includes problems uploading to concertina.net, images.yandex.com, images.bing.com, and sometimes images.google.com.
At the moment there is no issue uploading to imgur.com, so one of the many work-arounds is to upload to imgur, and then use that static URL as food for the image search engines, or as embedded links in online forums.
Had image uploading broken straightaway I think I would have made the Canvas connection sooner, what has happened is that site managers/developers have been slow to embrace the potentials of HTML 5, as have the developers of the APIs they use. As support becomes more common, more breakages will occur.
The clever thing would be for the APIs and host sites to test for Canvas support (trivial) and if not enabled then fallback to a simple HTTP POST, similar to limited jscript functionality handling for embedded devices, phones, ereaders.