Recaptcha and Gmail/Google account history

Are there any sort of guidelines as to what flags an account for receiving unreasonable amounts of correct captcha solve attempts? I'm not sure if this is considered top secret knowledge if someone cracks it, but an account that someone has that is solving hundreds of captchas manually or otherwise in an hour is going to get many more required solves than say someone who occasionally has to solve a captcha. There must be some sort of system to making accounts that fall in the latter category. I was considering setting up a captcha on a website of my own and experimenting with different account ages, IPs, usage type and history, etc. to see what gets an account flagged but if anyone has any knowledge on this topic it would be much appreciated!