when I want to register a new user and to write the words(not spam) do not appear.
see in you demo SJ Resorts it doesn't work also.

Dear mohamed hedi elhabib,

1. go to www.google.com/recaptcha/whyrecaptcha to get reCaptcha public key and reCaptcha private key.

2. check your key in Captcha - ReCaptcha plugin.

3. go to Components -> K2 -> Click on 'Parameters' button -> 'Advanced' tab -> Anti-spam Settings and put your key in there.

Thanks!