That setting would be really nice to have back. I think the vast majority of the users of this plugin are not concerned with spammers using automated OCR and would rather have easier captchas. Spammers going that far only going to go after the big sites that are not likely to being using this platform.
The simple captcha on Contact Form 7 stopped virtually 100% of spam messages on my other sites. Your plugin has some features that I need though.