This is how you add reCaptcha (the captcha system built by Google) to the Django’s comments framework.

Requirements

For this task you will need to build a custom module which depends on django-recaptcha-works. recaptcha-works provides a special Form field named “RecaptchaField”
and a decorator function “fix_recaptcha_remote_ip” which inserts the request’s REMOTE_ADDR (IP) into the request.POST data.

django-recaptcha-works can be downloaded from http://pypi.python.org/pypi/django-recaptcha-works/ or install it with:
pip install django-recaptcha-works

You also need a pair of reCaptcha keys from this address:

https://www.google.com/recaptcha/admin/create

Build a custom comment module

Create a new comment module, add it to INSTALLED_APPS and set a special settings COMMENTS_APP. The process is described on this page:

https://docs.djangoproject.com/en/dev/ref/contrib/comments/custom/

cd /path/to/your/project
mkdir my_comment_app

Make these changes to your settings file (usually settings.py):

INSTALLED_APPS = [
...
'my_comment_app',
...
]
COMMENTS_APP = 'my_comment_app'
RECAPTCHA_PUBLIC_KEY = 'public key'
RECAPTCHA_PRIVATE_KEY = 'private key'

recaptcha-works provides more settings, please check the settings.py from inside the recaptcha-works module.
Here are some interesting settings:

RECAPTCHA_USE_SSL = False
RECAPTCHA_OPTIONS = {
        'theme': 'white',
        'lang': 'en',
        'tabindex': 0,
}
RECAPTCHA_VALIDATION_OVERRIDE = False

Inside your new module “my_comment_app”, create these files:

__init__.py

from .forms import CustomCommentForm
def get_form():
return CustomCommentForm

forms.py

from django.contrib.comments.forms import CommentForm
from django.contrib.comments.models import Comment
from recaptcha_works.fields import RecaptchaField

class CustomCommentForm(CommentForm):
    recaptcha = RecaptchaField(label='Human test', required=True)
    def get_comment_model(self):
        return Comment

models.py

from django.db import models
from django.contrib.comments.models import Comment

class CustomComment(Comment):
    pass

urls.py

from django.conf.urls.defaults import patterns, include, url
from . import views

urlpatterns = patterns("",
    url(r'^post/$', views.custom_post_comment, name='comments-post-comment'),
    url(r'', include('django.contrib.comments.urls')),
)

views.py

from django.contrib.comments.views.comments import post_comment
from recaptcha_works.decorators import fix_recaptcha_remote_ip

def custom_post_comment(request, next=None, using=None):
    return fix_recaptcha_remote_ip(post_comment)(request, next, using)

You can download a sample of the module here.