I was tasked with implementing google reCaptcha into a magento site.

I looked at a few of the existing extension, but I was not happy with their implementations, so I decided to roll my own implementation of Google reCaptcha

For those who just want the code, and are not interested in how it was done, go grab the code off github (or install via composer)  - https://github.com/ProxiBlue/recaptcha