Recaptcha plugin problem

Hi all,

I am using radiant CMS and I am trying to create custom extension and
add recaptcha validation to it
but when I call
if not verify_recaptcha(:private_key => ‘aaaaaaaaaaa’)
#add error
end
I get: undefined method `verify_recaptcha’ for #Comment:0x4f4c460

Bellow is the full code for my model class

class Comment < ActiveRecord::Base

validates_presence_of :title, :author, :comment, :message =>
‘required’

validate :check_captcha

def check_captcha
if not verify_recaptcha(:private_key => ‘aaaaaaaaaaa’)
errors.add(:title, ‘def error’);
end
end

end

Please someone help

10x in adance,
Ilian Iliev