This uses some very slick computer vision techniques to do the signature extraction in variable lighting, and runs on AWS lambda for easy scalability. We'll be sending text messages to 300k Georgia voters on Monday (the first state where this is live), and will extend to 14 more states over the next month.
Check it out at https://VoteAmerica.com, or the backend code at https://github.com/vote/turnout
- disclaimer, I'm product director at VoteAmerica.com