Guyon
You don't need to use this to do that. And in fact this only saves png as I recall.
You can do it with vanilla c2. Add a Sprite and you can load a frame from URL. Then put the text on top like you want. Next you can you c2's snapshot action to capture it. Just set the viewport size to the image size you want to capture and scroll to the center of the location you want to capture.
Basically:
On click
--- set viewport size to 128x256
--- scroll to sprite
--- snapshot canvas as jpeg
On snapshot
--- browser: invoke download snapshoturl
You might need to add a wait 0 in there to get the view to update before capturing.