Inverse captchas or honeypots are a great idea. Just make a HTML input box with id=captcha, and hide it in some unconventional way in CSS so real users do not see it. If a bot was not deterred by seeing a captcha (a possibility), they would probably fill it. Whereas a real user won't.

This is an old trick. For example all MailChimp embed forms have dummy inputs that are visually hidden but might be filled in by bots.

Maybe not visually hidden, but practically invisible to human: imagine a text box with color #fffffe on a white background. Visually impossible to discern for most humans on most screens, but for a machine #fffffe is totally distinct from #ffffff, and fully visible if display != none.

As AI becomes more intelligent, you can prove humanity by exploiting our weaknesses.

(Another idea. Have a random image on a page actually be a text box with an image background. You cannot activate it if you focus on it, with your mouse or touch, but a bot doesn't need focus to change input.value.)

One pitfall: Screen readers will happily get caught on that. Of course, a11y concerns and bots tend to look similar in general, which is a perennial sticking point.

Please don't do this. This confuses and possibly prevents screen reader users from using your site.

This trick would not defeat GPT-4

Most bot creators check the target to compose steps before writing scripts so if they dont encounter captchas then there wont be a captcha handler

That solution just shows how bad the US tax system is, and most in Europe won't pass this (because it's already prefilled by their tax agencies or automatically witheld from their salaries).

I'm in Germany ... :-)

Unfortunately Australian tax forms take me a few minutes and are 90% prefilled by the app.