You can't use ReCaptcha (or any captcha) for ads. Captchas work because they prevent access to content users want until they solve the captcha.
If you put ads behind a captcha? Well in all honesty you're just doing a service to the user by hiding the ads behind a captcha they're never going to solve (even if they are not robots) because it's not in their best interest to do so.
> You can't use ReCaptcha (or any captcha) for ads. Captchas work because they prevent access to content users want until they solve the captcha.
If you've used ReCaptcha in the past few years [1] you might have noticed it often doesn't ask you to solve a captcha. The parent is describing using a similar approach of detecting bots to identify ad impressions that shouldn't be counted (spam).
If you put ads behind a captcha? Well in all honesty you're just doing a service to the user by hiding the ads behind a captcha they're never going to solve (even if they are not robots) because it's not in their best interest to do so.