I am not a DoS/spam expert but first things come to mind are : - Google account credibility (I have a very old Google account and this should provide me some tr

I am not a DoS/spam expert but first things come to mind are : - Google account credibility (I have a very old Google account and this should provide me some trust from Google's perspective) - Malicious word analysis in search queries - Browser/device information to determine authenticity of the search (if I am at home or connecting over a Tor network) - Gradually increase the response time for the queries On top of those, Google is a machine learning company and I am sure this process should be automated by now without requiring filling of any active captchas.