I will say up front that I have no good solution. That said, as a human, I hate captchas or anything else that makes me jump through hoops to do something that should be simple. The industry is punishing people to avoid bots or (whatever they are using them for in the instance), and yet it doesn't even work to accomplish that goal. Eliminate it all. Find something new. I wish I knew what to suggest. But it won't be anything at all like a captcha, stupid game to play, security questions, or anything like that.