I've been saying for years that I think 4chan is big enough to have their own captcha solution. It's very lazy to just use Google's reCaptcha and it's especially weird on a site with such an emphasis on Anonymous usage.
Google will know exactly how many times your IP posts on 4chan, and if you're logged into Google they attach those stats to your account. In combination with Google Analytics (also used by 4chan) they can figure out exactly what thread you make replies in. In fact by using timestamps they can figure out exactly which reply in a thread are yours and are able to profile your entire post history on the site, across all boards. So much for being Anonymous! No doubt they are hard at work to circumvent browser plugins that block trackers as well.
Wish people didn't hand them the keys to the web by using only their search engine, their browser, their e-mail, their site analytics, their video hosting services, their captcha solution. Even Microsoft are giving up now and will use Google's render engine for Edge.
(Remember that Google changed name to Alphabet and then started a new company named Google.)