user2442: Who or what decides that someone has enlightened himself?
It's just about an urge to know the point where/how enlightened one's or their followers approve that 'they are enlightened'. What happens immediately after that?

user5099: Ultimately one finds out if you are enlightened at the time of death and rebirth. :)

user-1: You can read about Nibbana and what Enlightment means
in this excellent Nibbana Sermon by  Venerable Bhikkhu K. Ñāṇananda
There are 33 sermons and they combine deep insight into the Dhamma with academic erudition, being based on copious quotations from the Pāli discourses that alternate with illustrative similes and useful indications for meditation practice.
http://www.seeingthroughthenet.net/files/eng/books/ms/html/Mind%20Stilled.htm#Mindstilled33
as an example from the above link on an arahant (one who is enlightened)

Tiṇakaṭṭhasamaṃ lokaṃ,
yadā paññāya passati,
mamattaṃ so asaṃvindaṃ,
'natthi me'ti na socati.

Translated:

"When one sees with wisdom,
This world as comparable to grass and twigs,
Not finding anything worthwhile holding onto as mine,
One does not grieve, saying: 'O! I have nothing!'"

Th 717, Adhimutta Theragāthā,
All the explanations are in the above link of the sermons  of Venerable Bhikkhu K. Ñāṇananda

user715: If there is beauty, there must be ugliness;
If there is right, there must be wrong.
Wisdom and ignorance are complementary,
And illusion and enlightenment cannot be separated.
This is an old truth, don't think it was discovered recently.
"I want this, I want that"
Is nothing but foolishness.
I'll tell you a secret -
"All things are impermanent!
Ryokan, One Robe, One Bowl: The Zen Poetry of Ryokan

user106: In the Palicanon I know two stories concerning this. The Buddha talks about when he himself (not yet judged by others) knew he's got the full awakening, the full wisdom - that was part of the story of his awakening process, and even a couple of self-assuring details are given.
And there are a lot of stories where people admit about themselves, that they are not yet fully awaken, one of the most prominent in the Parinibbans sutta, where Ananda, after 20 or more years of personal attendence with his master, says: my master goes away and I've not yet met my goal...           
When it comes to the other problem, that others should recognize/accept etc that one has reached the full enlightenment, then the medium of communication is the "lion's roar" (not specific to the Buddha-dharma, but as well as to the Samana/ascetics movement) I think DN 8 or DN 12 contains the Buddha's "lions-roar" and there is also one about Sariputta's "lions roar". That means, there is no licensing authority but the recognizing depends on whether the "lions-roar" is convincing. Devadatta is an example, where high achievements also can -later in the course of life- revert and a formerly really high ranked samana/bhikkhu can get horribly compromized.
There is no enlightenment-"license" and the above means also that such a "license" given by others cannot be perfect/permanent.               
If you ever vet yourself the experience of "whoa, now I know it really" - be it learning piano until mastership, ice-dancing or whatever then you likely shall understand that problem of "knowing-only-yourself" and the problem (is it one?) that to prove this to others is only by doing things masterly and convincingly. 

user5103: Only you can decide for yourself that you are truly enlightened.
Why: Because enlightenment is overcoming any and all ideals and dogma you impose upon yourself, including the need for enlightenment.

user-1: See this article "What Does It Mean To Be Enlightened?" by Ven. Bhikkhu Bodhi. 
In this article it is explained how the Buddha views enlightenment. Its based on a conversation the Buddha had with a Brahmin where the Buddha explains what is meant by a "Buddha".
This is the Buddhas own words:

“What has to be known, that I have known;
What has to be abandoned, that I have abandoned; 
What has to be developed, that I have developed; 
Therefore, O brahmin, I am a Buddha.”

In the article Ven. Bhikkhu Bodhi then takes each step and explains it, what it consists of and how it leads to enlightenment. I must say that this article is brilliantly written by Ven. Bhikkhu Bodhi.
Lanka

user254: I wish to read some incidents/examples. In the context of changed actions/way of living/thinking and perception making (Before enlightened vs. Now enlightened)
One theory is that there are Four stages of enlightenment.
The first of these four stage is stream-enterer or stream-winner,

In Buddhism, a Sotāpanna (Pali), Srotāpanna (Sanskrit; Chinese: 入流; pinyin: rùliú, Tibetan: རྒྱན་ཞུགས, Wylie: rgyun zhugs[1]), or "stream-winner"[2] is a person who has eradicated the first three fetters (sanyojanas) of the mind, namely self-view (or identity), clinging to rites and rituals, and skeptical doubt.

To try to understand that, I asked this question: What are examples of identity-view? It's not a great question (it's too long) but some people answered it well. If "abandoning identity-view" is a necessary characteristic of the first stage of enlightenment, you might like to read those answers to see what identity-view is.
Also the comments to this question, Are there any living enlightened people? explain there's a taboo (i.e. it breaks a Vinaya rule) about claiming to be enlightened (especially about claiming to be enlightened when you're not), so beware of that.

user471: In the Dona Sutta, Dona the brahmin observed the Buddha meditating under a tree and based on his demeanour, Dona thought that this cannot be an ordinary human being.
So, Dona asked the Buddha whether he is a god (deva), a celestial musician (gandhabba), a nature spirit (yakkha) or a human being. The Buddha answered "No" each time. Then when asked, "Then what sort of being are you?", the Buddha replied:
"The fermentations by which I would go
to a deva-state,
or become a gandhabba in the sky,
or go to a yakkha-state & human-state:
    Those have been destroyed by me,
    ruined, their stems removed.
Like a blue lotus, rising up,
unsmeared by water,
unsmeared am I by the world,
and so, brahman,
I'm awake."

So, the Buddha knows by himself that he is awake.
He knows by himself that he is not smeared by the world in the way that others are.
He knows by himself that all fermentations have been destroyed permanently and would no longer arise.
Here is my take on your question:
Imagine a scenario where a bunch of people are soundly asleep and suddenly one of them wakes up.
Now, he looks at the people around him who are still asleep, he knows for sure that he is awake and he knows for sure who else is sleeping and who else is awake.
But for those who are still asleep, could they know who is awake? Could they know what it means to be awake?
No, surely not.

2442: <p>Who or what decides that someone has enlightened himself?</p>

<p>It's just about an urge to know the point where/how enlightened one's or their followers approve that 'they are enlightened'. What happens immediately after that?</p>
 5099: <p>Ultimately one finds out if you are enlightened at the time of death and rebirth. :)</p>
 -1: <p>You can read about Nibbana and what Enlightment means
in this excellent Nibbana Sermon by  Venerable Bhikkhu K. Ñāṇananda</p>
<p>There are 33 sermons and they combine deep insight into the Dhamma with academic erudition, being based on copious quotations from the Pāli discourses that alternate with illustrative similes and useful indications for meditation practice.</p>
<p><a href="http://www.seeingthroughthenet.net/files/eng/books/ms/html/Mind%20Stilled.htm#Mindstilled33" rel="nofollow noreferrer">http://www.seeingthroughthenet.net/files/eng/books/ms/html/Mind%20Stilled.htm#Mindstilled33</a></p>
<p>as an example from the above link on an arahant (one who is enlightened)</p>
<blockquote>
<p>Tiṇakaṭṭhasamaṃ lokaṃ,</p>
<p>yadā paññāya passati,</p>
<p>mamattaṃ so asaṃvindaṃ,</p>
<p>'natthi me'ti na socati.</p>
</blockquote>
<p>Translated:</p>
<blockquote>
<p>&quot;When one sees with wisdom,</p>
<p>This world as comparable to grass and twigs,</p>
<p>Not finding anything worthwhile holding onto as mine,</p>
<p>One does not grieve, saying: 'O! I have nothing!'&quot;</p>
</blockquote>
<p>Th 717, Adhimutta Theragāthā,</p>
<p>All the explanations are in the above link of the sermons  of Venerable Bhikkhu K. Ñāṇananda</p>
 715: <p>If there is beauty, there must be ugliness;
If there is right, there must be wrong.
Wisdom and ignorance are complementary,
And illusion and enlightenment cannot be separated.
This is an old truth, don't think it was discovered recently.
"I want this, I want that"
Is nothing but foolishness.
I'll tell you a secret -
"All things are impermanent!</p>

<p>Ryokan, One Robe, One Bowl: The Zen Poetry of Ryokan</p>
 106: <p>In the Palicanon I know two stories concerning this. The Buddha talks about when <em>he himself</em> (not yet judged by others) knew he's got the full awakening, the full wisdom - that was part of the story of his awakening process, and even a couple of self-assuring details are given.<br>
And there are a lot of stories where people admit <em>about themselves</em>, that they are <em>not yet</em> fully awaken, one of the most prominent in the Parinibbans sutta, where Ananda, after 20 or more years of personal attendence with his master, says: my master goes away and I've not yet met my goal...           </p>

<p>When it comes to the other problem, that <em>others</em> should recognize/accept etc that one has reached the full enlightenment, then the medium of communication is the "lion's roar" (not specific to the Buddha-dharma, but as well as to the Samana/ascetics movement) I think DN 8 or DN 12 contains the Buddha's "lions-roar" and there is also one about Sariputta's "lions roar". That means, there is no licensing authority but the recognizing depends on whether the "lions-roar" is convincing. Devadatta is an example, where high achievements also can -later in the course of life- revert and a formerly really high ranked samana/bhikkhu can get horribly compromized.<br>
There is no enlightenment-"license" and the above means also that such a "license" given by others cannot be perfect/permanent.               </p>

<p>If you ever vet yourself the experience of "whoa, now I know it really" - be it learning piano until mastership, ice-dancing or whatever then you likely shall understand that problem of "knowing-only-yourself" and the problem (is it one?) that to prove this to others is only by doing things masterly and convincingly. </p>
 5103: <p>Only you can decide for yourself that you are truly enlightened.</p>

<p>Why: Because enlightenment is overcoming any and all ideals and dogma you impose upon yourself, including the need for enlightenment.</p>
 -1: <p><a href="http://bodhimonastery.org/what-does-it-mean-to-be-enlightened.html" rel="nofollow">See this article "What Does It Mean To Be Enlightened?" by Ven. Bhikkhu Bodhi.</a> </p>

<p>In this article it is explained how the Buddha views enlightenment. Its based on a conversation the Buddha had with a Brahmin where the Buddha explains what is meant by a "Buddha".</p>

<p>This is the Buddhas own words:</p>

<blockquote>
  <p>“What has to be known, that I have known;</p>
  
  <p>What has to be abandoned, that I have abandoned; </p>
  
  <p>What has to be developed, that I have developed; </p>
  
  <p>Therefore, O brahmin, I am a Buddha.”</p>
</blockquote>

<p>In the article Ven. Bhikkhu Bodhi then takes each step and explains it, what it consists of and how it leads to enlightenment. I must say that this article is brilliantly written by Ven. Bhikkhu Bodhi.</p>

<p>Lanka</p>
 254: <p><strong>I wish to read some incidents/examples. In the context of changed actions/way of living/thinking and perception making (Before enlightened vs. Now enlightened)</strong></p>

<p>One theory is that there are <a href="http://en.wikipedia.org/wiki/Four_stages_of_enlightenment" rel="nofollow noreferrer">Four stages of enlightenment</a>.</p>

<p>The first of these four stage is stream-enterer or <a href="http://en.wikipedia.org/wiki/Sot%C4%81panna" rel="nofollow noreferrer">stream-winner</a>,</p>

<blockquote>
  <p>In Buddhism, a Sotāpanna (Pali), Srotāpanna (Sanskrit; Chinese: 入流; pinyin: rùliú, Tibetan: རྒྱན་ཞུགས, Wylie: rgyun zhugs[1]), or "stream-winner"[2] is a person who has eradicated the first three fetters (sanyojanas) of the mind, namely self-view (or identity), clinging to rites and rituals, and skeptical doubt.</p>
</blockquote>

<p>To try to understand that, I asked this question: <a href="https://buddhism.stackexchange.com/q/5862/254">What are examples of identity-view?</a> It's not a great question (it's too long) but some people answered it well. If "abandoning identity-view" is a necessary characteristic of the first stage of enlightenment, you might like to read those answers to see what identity-view is.</p>

<p>Also the comments to this question, <a href="https://buddhism.stackexchange.com/q/3058/254">Are there any living enlightened people?</a> explain there's a taboo (i.e. it breaks a Vinaya rule) about claiming to be enlightened (especially about claiming to be enlightened when you're not), so beware of that.</p>
 471: <p>In the <a href="http://www.accesstoinsight.org/tipitaka/an/an04/an04.036.than.html" rel="nofollow">Dona Sutta</a>, Dona the brahmin observed the Buddha meditating under a tree and based on his demeanour, Dona thought that this cannot be an ordinary human being.</p>

<p>So, Dona asked the Buddha whether he is a god (deva), a celestial musician (gandhabba), a nature spirit (yakkha) or a human being. The Buddha answered "No" each time. Then when asked, "Then what sort of being are you?", the Buddha replied:</p>

<pre><code>"The fermentations by which I would go
to a deva-state,
or become a gandhabba in the sky,
or go to a yakkha-state &amp; human-state:
    Those have been destroyed by me,
    ruined, their stems removed.
Like a blue lotus, rising up,
unsmeared by water,
unsmeared am I by the world,
and so, brahman,
I'm awake."
</code></pre>

<p>So, the Buddha knows by himself that he is awake.</p>

<p>He knows by himself that he is not smeared by the world in the way that others are.</p>

<p>He knows by himself that all fermentations have been destroyed permanently and would no longer arise.</p>

<p>Here is my take on your question:</p>

<p>Imagine a scenario where a bunch of people are soundly asleep and suddenly one of them wakes up.</p>

<p>Now, he looks at the people around him who are still asleep, he knows for sure that he is awake and he knows for sure who else is sleeping and who else is awake.</p>

<p>But for those who are still asleep, could they know who is awake? Could they know what it means to be awake?</p>

<p>No, surely not.</p>
