Yeah, I know that is dangerous activity; but, indulge me, please.
What is it that Captchas are trying to stop? Is it really "automation" vs "real people" or is it related to something practical like drain on system resources that comes with automation banging the open ports at speeds you and I cannot imagine? The resource related reason makes more sense to silly old me. So, what would I do to detect resource robbers from more legitimate uses human manual or human directed single accesses? I'd burn a few cycles on the resource hog's machine with a complex javascript, perhaps do a brief bit of mining. Two or three seconds of that while the Captcha is putting itself together is a resource burn on the endless supply of search engines and AI training runs. The trick is to figure out the maximum burn the r-hogs will tolerate. Maybe you should double it? Then build that into your captcha building on the challenge page. The r-hogs go away. The smart ones log your machine as annoying. And your machine stays open for legitimate uses.
Does that sound close to the truth to you or am I just another old fruitcake on the net who likes the thought of r-hogs paying for access via a little bitcoin mining.
{^_-}