As I understand it, reCAPTCHA now relies heavily on metadata to determine if someone is a bot. Probably stuff like their IP address, browser information, geographic location, internet speed. Then it predicts how likely they are to be a spam bot and sends them a much harder CAPTCHA if so. And they change the interface to throw off bots.
The average person who just wants to automate filling out your website form is still blocked, so it's not useless.
There is some recent research that suggests you can make images which are very hard for neural networks to identify, but still easy for humans.
Here is an example: http://i.imgur.com/K6AQRkV.png The digits on the right are just slightly changed to be harder for NNs to recognize.
For comparison, this is the amount of random noise needed to have the same effect as their method: http://i.imgur.com/Asnf2L8.png
The average person who just wants to automate filling out your website form is still blocked, so it's not useless.
There is some recent research that suggests you can make images which are very hard for neural networks to identify, but still easy for humans.
Here is an example: http://i.imgur.com/K6AQRkV.png The digits on the right are just slightly changed to be harder for NNs to recognize.
For comparison, this is the amount of random noise needed to have the same effect as their method: http://i.imgur.com/Asnf2L8.png