diff --git a/boards/forms.py b/boards/forms.py
--- a/boards/forms.py
+++ b/boards/forms.py
@@ -4,7 +4,7 @@ from django import forms
 from django.forms.util import ErrorList
 from boards.models import TITLE_MAX_LENGTH
 from neboard import settings
-
+from boards import utils
 
 class PlainErrorList(ErrorList):
     def __unicode__(self):
@@ -67,9 +67,6 @@ class PostForm(forms.Form):
             self._errors['image'] = self.error_class([error_message])
 
 
-class PostCaptchaForm(PostForm):
-    captcha = CaptchaField()
-
 
 class ThreadForm(PostForm):
     regex_tags = re.compile(ur'^[\w\s\d]+$', re.UNICODE)
@@ -91,9 +88,47 @@ class ThreadForm(PostForm):
         return cleaned_data
 
 
+class PostCaptchaForm(PostForm):
+    captcha = CaptchaField()
+
+    def __init__(self, *args, **kwargs):
+        self.request = kwargs['request']
+        del kwargs['request']
+
+        super(PostCaptchaForm, self).__init__(*args, **kwargs)
+
+    def clean(self):
+        cleaned_data = super(PostCaptchaForm, self).clean()
+
+        success = self.is_valid()
+        utils.update_captcha_access(self.request, success)
+
+        if success:
+            return cleaned_data
+        else:
+            raise forms.ValidationError("captcha validation failed")
+
+
 class ThreadCaptchaForm(ThreadForm):
     captcha = CaptchaField()
 
+    def __init__(self, *args, **kwargs):
+        self.request = kwargs['request']
+        del kwargs['request']
+
+        super(ThreadCaptchaForm, self).__init__(*args, **kwargs)
+
+    def clean(self):
+        cleaned_data = super(ThreadCaptchaForm, self).clean()
+
+        success = self.is_valid()
+        utils.update_captcha_access(self.request, success)
+
+        if success:
+            return cleaned_data
+        else:
+            raise forms.ValidationError("captcha validation failed")
+
 
 class SettingsForm(forms.Form):
-    theme = forms.ChoiceField(choices=settings.THEMES, widget=forms.RadioSelect)
\ No newline at end of file
+    theme = forms.ChoiceField(choices=settings.THEMES, widget=forms.RadioSelect)
diff --git a/boards/models.py b/boards/models.py
--- a/boards/models.py
+++ b/boards/models.py
@@ -8,6 +8,7 @@ from django.db import models
 from django.http import Http404
 from django.utils import timezone
 from markupfield.fields import MarkupField
+from threading import Thread
 
 from neboard import settings
 import thumbs
diff --git a/boards/templates/boards/posting_general.html b/boards/templates/boards/posting_general.html
--- a/boards/templates/boards/posting_general.html
+++ b/boards/templates/boards/posting_general.html
@@ -130,6 +130,7 @@
             </div>
             <div class="form-row">
                 {{ form.captcha }}
+                <div class="form-errors">{{ form.captcha.errors }}</div>
             </div>
         </div>
         <div class="form-submit">
diff --git a/boards/templates/boards/thread.html b/boards/templates/boards/thread.html
--- a/boards/templates/boards/thread.html
+++ b/boards/templates/boards/thread.html
@@ -84,6 +84,7 @@
                 </div>
                 <div class="form-row">
                     {{ form.captcha }}
+                    <div class="form-errors">{{ form.captcha.errors }}</div>
                 </div>
             </div>
 
diff --git a/boards/utils.py b/boards/utils.py
--- a/boards/utils.py
+++ b/boards/utils.py
@@ -1,14 +1,64 @@
 """
 This module contains helper functions and helper classes.
 """
+
 from neboard import settings
+import time
 
 
-def check_if_human(request):
+KEY_CAPTCHA_FAILS = 'key_captcha_fails'
+KEY_CAPTCHA_DELAY_TIME = 'key_captcha_delay_time'
+KEY_CAPTCHA_LAST_ACTIVITY = 'key_captcha_last_activity'
+
+
+def need_include_captcha(request):
     """
     Check if request is made by a user.
     It contains rules which check for bots.
     """
 
-    # FIXME: need to insert checking logic
-    return not settings.ENABLE_CAPTCHA
+    if not settings.ENABLE_CAPTCHA:
+        return False
+
+    enable_captcha = False
+
+    #newcomer
+    if KEY_CAPTCHA_LAST_ACTIVITY not in request.session:
+        return settings.ENABLE_CAPTCHA
+
+    last_activity = request.session[KEY_CAPTCHA_LAST_ACTIVITY]
+    current_delay = int(time.time()) - last_activity
+
+    delay_time = (request.session[KEY_CAPTCHA_DELAY_TIME]
+                  if KEY_CAPTCHA_DELAY_TIME in request.session
+                  else settings.CAPTCHA_DEFAULT_SAFE_TIME)
+
+    if current_delay < delay_time:
+        enable_captcha = True
+
+    print 'ENABLING' + str(enable_captcha)
+
+    return enable_captcha
+
+
+def update_captcha_access(request, passed):
+    """
+    Update captcha fields.
+    It will reduce delay time if user passed captcha verification and
+    it will increase it otherwise.
+    """
+    session = request.session
+
+    delay_time = (request.session[KEY_CAPTCHA_DELAY_TIME]
+                  if KEY_CAPTCHA_DELAY_TIME in request.session
+                  else settings.CAPTCHA_DEFAULT_SAFE_TIME)
+
+    print "DELAY TIME = " + str(delay_time)
+
+    if passed:
+        delay_time -= 2 if delay_time >= 7 else 5
+    else:
+        delay_time += 10
+
+    session[KEY_CAPTCHA_LAST_ACTIVITY] = int(time.time())
+    session[KEY_CAPTCHA_DELAY_TIME] = delay_time
diff --git a/boards/views.py b/boards/views.py
--- a/boards/views.py
+++ b/boards/views.py
@@ -16,18 +16,21 @@ import neboard
 def index(request, page=0):
     context = RequestContext(request)
 
-    threadFormClass = (ThreadForm
-                       if utils.check_if_human(request)
-                       else ThreadCaptchaForm)
+    if utils.need_include_captcha(request):
+        threadFormClass = ThreadCaptchaForm
+        kwargs = {'request': request}
+    else:
+        threadFormClass = ThreadForm
+        kwargs = {}
 
     if request.method == 'POST':
         form = threadFormClass(request.POST, request.FILES,
-                               error_class=PlainErrorList)
+                               error_class=PlainErrorList, **kwargs)
 
         if form.is_valid():
             return _new_post(request, form)
     else:
-        form = threadFormClass(error_class=PlainErrorList)
+        form = threadFormClass(error_class=PlainErrorList, **kwargs)
 
     threads = Post.objects.get_threads(page=int(page))
 
@@ -119,16 +122,20 @@ def tag(request, tag_name, page=0):
 def thread(request, post_id):
     """Get all thread posts"""
 
-    postFormClass = (PostForm if utils.check_if_human(request) else
-                     PostCaptchaForm)
+    if utils.need_include_captcha(request):
+        postFormClass = PostCaptchaForm
+        kwargs = {'request': request}
+    else:
+        postFormClass = PostForm
+        kwargs = {}
 
     if request.method == 'POST':
         form = postFormClass(request.POST, request.FILES,
-                             error_class=PlainErrorList)
+                             error_class=PlainErrorList, **kwargs)
         if form.is_valid():
             return _new_post(request, form, post_id)
     else:
-        form = postFormClass(error_class=PlainErrorList)
+        form = postFormClass(error_class=PlainErrorList, **kwargs)
 
     posts = Post.objects.get_thread(post_id)
 
diff --git a/neboard/settings.py b/neboard/settings.py
--- a/neboard/settings.py
+++ b/neboard/settings.py
@@ -187,9 +187,12 @@ SITE_NAME = 'Neboard'
 THEMES = [
     ('md', 'Mystic Dark'),
     ('sw', 'Snow White') ]
+
 DEFAULT_THEME = 'md'
 
 POPULAR_TAGS = 10
 LAST_REPLIES_COUNT = 3
 
-ENABLE_CAPTCHA = False
\ No newline at end of file
+ENABLE_CAPTCHA = True
+# if user tries to post before CAPTCHA_DEFAULT_SAFE_TIME. Captcha will be shown
+CAPTCHA_DEFAULT_SAFE_TIME = 30  # seconds
\ No newline at end of file