ruby script/plugin install http://svn.ambethia.com/pub/rails/plugins/recaptcha/

You‘ll want to add your public and private API keys in the environment variables RECAPTCHA_PUBLIC_KEY and RECAPTCHA_PRIVATE_KEY, respectively. You could also specify them in config/environment.rb if you are so inclined. Exceptions will be raised if you call these methods and the keys can‘t be found.

recaptcha_tags
================
Some of the options available:

:ssl: Uses secure http for captcha widget (default false)
:noscript: Include content (default true)
:display: Takes a hash containing the theme and tabindex options per the API. (default nil)
:public_key: Your public API key, takes precedence over the ENV variable (default nil).
:error: Override the error in +session[:recaptcha_error]+ (default nil).

verify_recaptcha
================
This method returns true or false after processing the parameters from the ReCAPTCHA widget. Why isn‘t this a model validation? Because that violates MVC. Use can use it like this, or how ever you like. Passing in the ActiveRecord object is optional, if you do—and the captcha fails to verify—an error will be added to the object for you to use.

        respond_to do |format|
          if verify_recaptcha(@post) && @post.save
            # ...
          else
            # ...
          end
        end

There is currently no advanced documentation for this plugin.