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Is there any close or best open source solutions as Google's Invisible reCAPTCHA V2? And also as Google's regular reCAPTCHA V2(checkbox one)?
SecurImage or phpcaptcha is open source alternative to Google reCaptcha v2. But I don't think there's any alternative to the Invisible reCaptcha yet. You can refer to This for some good alternatives for reCaptcha v2 (though most of them are not open source).
I have yet to find any pre-assembled free code implementations, but my favourite suggestions so far for replacing reCaptcha is the honeypot technique. The concept is that webmasters add fields to their forms that are invisible to human users, but visible to bots. When bots fill in these invisible fields, they reveal that they're not human, and the forms can be safely discarded. More details here: http://ezinearticles.com/?Captchas-Considered-Harmful---Why-Captchas-Are-Bad-And-How-You-Can-Do-Better&id=1104207
... and some discussion of implementation here: https://www.thryv.com/blog/honeypot-technique/
I like this because of the way it shifts the burden of proof. Instead of requiring users to perform annoying extra tasks to prove they are human, they are presumed to be human, unless they reveal themselves to be bots. Also, 'are you a human' captchas, are known to make it difficult (if not impossible) for some special needs users to access websites, so this is another good reason to find a replacement for them.
There are definitely much better solutions than reCAPTCHA out there now. I like solutions that focus on user experience. Another great option I don’t see listed here is Human Presence. Human Presence uniquely analyzes user behavior invisibly in the background on your site and determines whether the user is human or bot using proprietary machine learning algorithms to measure the user's actual behavior across dozens of different data points...keyboard strokes, mouse movements, micro gestures, etc.
The best part is that real users on a website are never punished with turing tests like CAPTCHAs or math problems. The Human Presence API can be configured to check the session and make sure the user is human before processing forms, comments, wishlists, shopping carts, or even page loads so that only bots are blocked but legitimate users continue on about their business as without any knowledge of the technology.
