I’ve developed a browser extension that automatically solves reCAPTCHA:

no API keys
no registrations anywhere
no account top-ups anywhere

How it works: there’s a very lightweight neural network inside, trained on all existing reCAPTCHA classes. The extension detects when a reCAPTCHA appears on a webpage, clicks the checkbox, and handles the image selections on its own. The neural network is very “thin,” so it barely uses any CPU. Accuracy on 3×3 captchas is almost perfect; on 4×4, it’s acceptable.

The extension is free and available in stores:
Chrome Web Store: https://chromewebstore.google.com/detail/free-ai-recaptcha-solver/iomcoelgdkghlligeempdbfcaobodacg

Firefox Add-ons: https://addons.mozilla.org/en-US/firefox/addon/captchaplugin/

A couple of downsides:

It’s fairly large — about 76 MB (the first version was over 500 MB).
The extension sends reports with encountered images to its server. This can be disabled: go to “Reports” and turn off “Enable reports.”