Can bots still go through a captcha registration system?

Yes. I knew someone who published a PHP-based neural network on their site around 2010 or so that could read CAPTCHAs who got his site hacked because it was a little over the line.

The main technique used by Re:CAPTCHA is web tracking; the best sign that somebody is not a bot is to find a set of tracking cookies that can be linked up to a long history of ads served even if never clicked on.

A captcha can help in some scenarios, but they can be easily bypassed most of the time if anyone really wanted to.