I had simple questions you can answer with text on my site for years, and I had no spam problem whatsoever.
I am not convinced that training google’s image recognition algorithms is the only way to solve the captcha problem
I am not convinced that training google’s image recognition algorithms is the only way to solve the captcha problem
I spent days trying it out with screen readers and tweaking it to work with as many as possible.
To me, it sounds like your system is just security by obscurity. It wouldn't scale, if it did become used prevalently then it would be very easy for bots to circumvent.
It won’t scale, because it mustn’t scale. It is a dead simple solution to a complicated problem and works as long as it works, without selling your user data and brainpower toone of the biggest tech companies there is.
If it should happen that the spam bots overcome it or your site becomes big enough to be targeted you just change it for something stricter, stronger or more sophisticated.