If I were to enter the CAPTCHA-breaking business today, I'd probably use one of these services at first to collect a million correct solutions for $800, and then use that dataset to train my AI.
Once the AI is good enough, I can buy a bunch of used GPUs from former ethereum miners, throw them in a cheap DC somewhere, and undercut everyone else! Sounds like a decent side project that could yield a bit of passive income. Somebody else has probably done it already. Maybe OP is that somebody.
This is what hCaptcha is currently doing, they are switching the image category every 24-72 hours.
How useful is it? Not very. Modern ML models such as mobilenet, resnet or yolo require only a few hundred images for it to be accurate to solve those captchas.
You don't need few million samples, with 500-700 images per category you are more than ready to solve current captchas.
Once the AI is good enough, I can buy a bunch of used GPUs from former ethereum miners, throw them in a cheap DC somewhere, and undercut everyone else! Sounds like a decent side project that could yield a bit of passive income. Somebody else has probably done it already. Maybe OP is that somebody.