That’s a side project, and doesn’t explain all the services that use it without images.
Regardless, you always have to connect to 3 different domains - typically the website itself, google.com and gstatic.com. These 3 domains allow for very accurate triangulation across the internet, and each one will fingerprint your browser. They might not know your bank account number or social media account name, but they know that someone using your browser banks with this bank and has an account on that social media, along with thousands of other data points.
CAPTCHA: Bot vs. Human. Bot wins. (feddit.de)
arxiv.org/pdf/2307.12108.pdf