google recaptcha
google recaptcha https://www.google.com/recaptcha/ doc https://developers.google.com/recaptcha/docs/start New reCaptcha with jQuery Validation Plugin http://stackoverflow.com/questions/29563822/new-recaptcha-with-jquery-validation-plugin How can I validate google reCAPTCHA v2 using javascript/jQuery? http://stackoverflow.com/questions/27902539/how-can-i-validate-google-recaptcha-v2-using-javascript-jquery