Try this one:
https://gist.github.com/1747707
It basically uses the toDataURL() method to get the image data of the canvas.
It basically uses the toDataURL() method to get the image data of the canvas.
think there is something coming with BlobBuilder and FileSaver, but i haven't hat time yet to give it a spin http://dev.w3.org/2009/dap/file-system/file-writer.html#idl-... and an example here http://updates.html5rocks.com/2011/08/Saving-generated-files...