Proton, the Swiss company that develops privacy-focused online services such as email, has developed its very own CAPTCHA service to help discern between
Encryption is generally "open source" and that's what makes is strong. Security does not come from people not knowing how things work, but by having properly designed things that work whether people know how they work or not.
It doesn't seem to me like encryption is comparable here. With encryption we have known algorithms that are harder to reverse than initially run. This is a completely different problem, where many inputs are taken and some algorithm has to decide if they are human or not. What digital task can a human do that a robot can't in the same way, especially if the robot knows exactly the measures it should aim for?
exactly what recaptcha does, for example. Knowing that you have to type a word because a computer failed to identify which word is it makes creating a program that does that no easier. Same with the image ones. While criptography is a different problem, the argument is the same: you want something that can be verified to be hard to break otherwise someone will eventually figure it out
If you have a known algorithm for generating those hard-to-read images, then it really wouldn't be that difficult to generate a large enough set yourself to train a custom ML model to solve them. The same would apply to audio challenges.
Only one person would need to do it then they could share the process, potentially automating others being able to bypass as well.
I like the idea of captcha being open, but unlike encryption as far as I know we don't have a starting point on something that is actually easier for humans when all information is available. Until something like that exists, open sourcing to implement and improve it doesn't make sense if you want an effective product.
The text is not generated. It's from photos of books that failed ocr. The photos are then distorted to make it even harder in order to become that captcha. 2 words are used 1 is a control (to know if the response is correct), the other is one they what to know what says (to add to the pool of words and finish digitizing the book).