In this you can see how to make google captcha valifation in HTML form(s).In this we can see two methods of validation.

Method 1 : If using Jquery for form validation ,do the following stpes

STEP 1 :  Add the following script at before the </head> section

<script src="https://www.google.com/recaptcha/api.js"></script>

STEP 2 : Before that, register your site and get the sitekey for you website.

to get the key click here  and sign in your gmail account.

STEP 3 : Add the following code in your form where do you want to display the captcha.

<div class="g-recaptcha" data-sitekey="your-site-key"></div>

add you site key in above code.

STEP 4 : If you are using Jquery validation for your form add the below in your validation section. ie.after the variable declarations

if (grecaptcha.getResponse() == ""){

$("#error_message").show().html("ReCaptcha was not validated");

}

after the form submission give below to reset the captcha

grecaptcha.reset();

Method 2 :

If you aren’t using jquery validation and need js validation just add the below script in you html page or js file.

<script type="text/javascript">
function validateform(){
var captcha_response = grecaptcha.getResponse();
if(captcha_response.length == 0)
{
 // Captcha is not Passed
alert("Captcha validation failed");
 return false;
}
else
{
 // Captcha is Passed
 return true;
}
}
</script>

NOTE : Add the onsubmit=”return validateform();” in the form like below

 <form action="contact.php" method="post"  onsubmit="return validateform();">