Is there a reliable captcha or other protection against spambots?

Question

CAPTCHA

Since the beginning of 2015, spam on several of our projects has become very aggravated. Spam is typical - some kind of advertisement on how to quit smoking and something about girls. A spam text search showed that this is not only our problem, but also heaps of projects where there are forums / comments. For this reason, I concluded that this was not a targeted attack on us, but some kind of universal bot.
All our sites have registration with different captchas, which these bots successfully bypass. I will list what protections we used and they did not help:

• Standard graphic captcha
  
• Simple digital captcha like a+b=c
  
• Unique text captcha (a set of simple questions, such as "what color is the grass", "who wrote Oginsky's polonaise", etc.)
  
• Spam text pattern protection (after several bots caught, spam texts change). Yes, and it’s inconvenient, every time you enter spam text somewhere
  
• Trap fields that only populate bots hidden via css or js
  
• Simple JS captcha (registration without js support will not work).
  
• The time between opening the registration form and filling it out was analyzed - everything is within the real values.
  
• Randomization of field names in the registration form.
  
• Stopforumspam service check. Stands on one of the sites - does not help.
  
• Account activation via email. Activate without problems.
  

On sites that allow registration and authorization through social networks, sometimes spammers register through mail.ru or VK.
While we are at a slight impasse, because it is not clear how to defend further. I propose to discuss additional features of protection against spam bots. Perhaps someone has already encountered these same bots and was able to successfully cut them off. I would love to hear suggestions and ideas.

Answer 1

On several of our projects, there was a problem of spam on application forms, they were cut off in many ways, the main one, they blocked pools of IP addresses from which attacks were carried out, in fact, there were not so many of them.

Answer 2

stumper.ru/use/isText