Are you getting a lot of spam emails from your website or blogs through the contact form?. Then its time to think to add a security check to avoid these spam or robotic submissions.
Steps to Integrate in your website :
1.Signup with google and create a new reCaptcha Account for your Site
2.You will get Site key and a Secret Key
Use the Site Key in your web page form while accepting the input from the user
3.Use the secret key to validate the submission by sending a request to google server from the server side after submission using following details
Parameters (GET) :
secret (required) : “YOUR SITE SECRET KEY”
response (required) : The value of ‘g-recaptcha-response’.
remoteip : The end user’s ip address.
Security : I’m not a Robot :
Google implemented this last December 2014. Instead of asking the users to verify the image or text, the user can simply click the checkbox to confirm whether the user is not a Robot. But sometimes if you keep submitting the form multiple times, google suspects this action and double checks the submission using the Traditional CAPTCHA like prompting for user Input with Images & Text.
Here some screenshots how Google handles the reCaptcha when it suspects the multiple submission activity :