C3.js[0] has a built in image exporter[1] you can use from the command line if you want to generate chart images programatically. I use something similar that I wrote just before this became part of C3 to generate the chart and upload it to S3. Then my email links to that image. Works very nicely!

0: http://c3js.org/

1: https://github.com/masayuki0812/c3/blob/14e92c54f9286bf28ff4...