ReCaptcha always asking for extra verification?

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For a project, I recently installed the new 2.0 version of ReCaptcha. I added the keys and secret to the Developer Panel, and installed the widget in my form.

It works perfectly, but with one little problem: The Captcha is always asking for a second verification. It's nice to users if they only see the green tick, but after clicking the Captcha, it comes with the extra picture verification...

So what's the problem here? Google not trusting my IP? How to check?

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Solution

According to a WIRED article, Google is (amongst other indications) using IP addresses and cookies to recognize you.

Instead of depending upon the traditional distorted word test, Google’s “reCaptcha” examines cues every user unwittingly provides: IP addresses and cookies provide evidence that the user is the same friendly human Google remembers from elsewhere on the Web. And Shet says even the tiny movements a user’s mouse makes as it hovers and approaches a checkbox can help reveal an automated bot.

In your browser settings, you have most likely disabled third-party cookies, which will prevent Google from recognizing you. Add *.google.com to your whitelist, and the image-based verification won't show up again.