I often get asked whether Divi Booster has the ability to add Google's reCaptcha to the Divi contact form. It doesn't at the moment (though if you'd find that useful, let me know in the comments).
There are however a couple of existing plugins which can be used to integrate reCaptcha with Divi. They are:
I've used the one by Trumani and it worked well. I haven't tried the Bestwebsoft one yet.