How to use CAPTCHA

Free captcha script downloads, captcha tutorials and information.
Add captcha to your website by yourself in less than 20 minutes
and no php nor HTML knowledge needed.

captcha logo

c.a.p.t.c.h.a. =
completely automated public Turing test to tell computers and humans apart.

In normal speak captcha is used to protect web forms against spammers.

How to understand, use and implement
captcha to protect your web site against
spam and form spamming.

captcha instruction guide


On this captcha web site you will find:

examples of captcha at work,
useful information on how to use captcha,
captcha forms and captcha code,
free captcha downloads for your own use,
methods and techniques of implementing captcha,
information on how to stop or at least downsize spam
with the use of captcha .

If you are a captcha beginner start here and just continue reading this page.

Before you continue - try this - an example of how easy it is to implement the here suggested captcha solution - a step by step captcha implementation video tutorial ...(opens in a new browser window )

If you have php know-how, scroll down to the index section.

How to use captcha : part 1 of 6

What is Captcha ?

Captcha is an acronym - explained later, but mainly captcha is a simple verification system made up of:
1] the captcha image and the captcha code that generates it
a computer generated image, sometimes distorted and in most cases the image is a .png or .jpg which usually consist of a background and letters and numbers of a different colour that appear on that background

2] a form field into which the code one sees in the captcha image must be inserted - and an enter button
The field can either be part of a mail form, or a separate entity and is directly connected codewise to the captcha generated image.

3] a separate code, probably in PHP, which checks that the code inserted manually into the field was correct
Once the user enters the code he sees in the image, the verification code checks to see if the code entered was correct, and if yes the form is sent off correctly or the user is redirected to the captcha protected pages, or in the case of an error, the form won't be sent, the captcha verification code generates an error, and indicates to the user to try again either by refreshing his browser, or by clicking a button to regenerate new captcha code

Try this example of a captcha protected page
[ opens in a new browser window ]

So, if you went to the using captcha link above and tried it - then now you know how captcha works from the user's side.

Whilst you're at it, also try this different captcha image generating sequence:
example on captcha implementation
[ opens in a new browser window ]

So ....

In the captcha examples above, you will have noticed that this is maybe a strange way of implementing captcha, as first the user goes to a link that takes him to the captcha page, and after verification is taken to another page, which could have been the main form we wanted the user to fill in, but in our case was yet another link page which then can take the user wherever one likes.
There is a certain logic to this and will be explained later.

While we're at it, you may have also noticed that the Captcha examples show above are all pretty small. No problem and check out this Captcha example where not only the image is bigger and more readable, but we can also modify the background color, font size, thickness of the lines, angle of font and the lines etc.
Will open a new browser window - when done just close the window and continue reading here.

How can Captcha help against spam?

Captcha can be a great help in downsizing or diminishing form spamming.
[ form spamming is when bots go around the web, find forms and either hijack them - meaning they send thousands of spam emails through that form or - in the least - send at least one e-mail through that form.
Or, they fill in the form and sign up for hundred free e-mail accounts, or order hundreds of services and even products.
On our captcha links page you will find links to captcha related articles around the web.
Bots can also harvest any e-mail addresses inside the form's html code - and this is where captcha is not much of help - but on this site you will also find a solution to this problem too.]

So if you use Captcha on your web site forms, this can help in stopping some bots and making life harder for other bots in accessing or using your forms.


How does Captcha try to fool the spam bots ?

Well, internet robots, the so called bots, which are programs made with the purpose of scouring the web for forms and e-mail addresses, are a bit different to human eyeballs.

When the human user enters a captcha page and sees a code generated image - usually numbers and letters - he must insert this code, by typing the same numbers or letters in the image into a field and if he has copied correctly - he will be allowed to click the send button and either send the form or proceed to other web pages.

Human eyeballs have a much more sophisticated system of recognizing complex images and still be able to extract the numbers and letters which are in the image.

The bot on the other hand, does not have such sophistication, and mostly is programmed to extract e-mail addresses from the html code of a web page.
But because even the bots have become more sophisticated and some of them have image recognition algorithms programmed into them and can read even images with numbers and letters, this is why captcha created images are usually also a bit distorted or have dots and lines along with the numbers to try to confuse the bot as much as possible.

This basically means that a human can pass through a captcha protected page or form but a bot will have a harder task.

This because a bot has difficulty in reading and then typing in what it first saw on a graphical image.
Please note - the keyword here is 'harder task'.

The bot, via the page body and page source code can figure out where the fields are etc, but it has a harder task of figuring out an image, which is not part of the code and hence captcha serves to fool or impede the bot in his task since if the bot has figured out all the form fields and manages to send the form without the correct captcha generated code - an error will be generated as the graphical image code is missing and the form will not get sent.

But...and this is a big but....
the system of creating a web form in pure HTML does NOT prohibit the bot in getting to the actual form page html source and finding the email address and hence if implemented this way, captcha can prevent the bot from sending the form BUT NOT from harvesting any e-mail addresses contained inside the page source.

This is why there are two ways to go about protecting your web forms against spam bots.
The one easy method explained on this website is for the non programmer whereby you simply create a Captcha verification system BEFORE the user - or the spam bot - gets to the actual web form.
The second system is that one uses captcha protected forms ( the captcha residing on the same page as the form) but with the form and verification system all done in php, which is code that is not as easily accessed neither by the bot nor by the eyeball.


Why do I need Captcha ?

We all need captcha because spammers send automatic bots to scour the web, find forms, and use them for spamming.
In very malicious scenarios the bots will send thousands of spams through your web site form.


Is captcha easy to use and to implement ?

Yes and no.
If you have minimal PHP basics, or even other similar programming or scripting language basics, implementing captcha is easy.
Meaning that you will easily be able to tailor the many captcha scripts around to your needs and actually understand what you are doing.

If you have no programming knowledge, the you can still implement captcha and this is why this website came to be.
This web site is aimed at php or HTML idiots like myself and probably every third one of yourselves reading this who are not versed in php etc, don't want to be - and just want the fastest, easiest and most functional solution available at this moment to stop form spamming, and even form email address harvesting.


Who can use and implement captcha ?

If I can, so can you - and on this website you will be able to see how I implemented captcha and how it works for me.
Also, and this was the MAIN reason for me wasting my time in setting up this website, I will show you a very easy method in implementing captcha on your website without having to redo, re design or build from scratch your existing forms that you may already have.

Call this the Captcha for dummies website if you like.


Captcha pros and cons

The pros of using captcha have already been discussed and in a nutshell, captcha can help combat automatic bots from spamming your web site form, harvesting e-mail addresses or worse.
But, captcha is not a spammer proof system 100% so I wouldn't put your bank account details or credit card pin behind a captcha protected page if I were you.
The main cons or downside of captcha, now being feverently discussed on forums and blogs not to mention the World Wide Web Consortium are the fact that in many cases the captcha generated and distorted image turns out to be so much distorted that the human user has difficulty in recognizing it.
But this is a pretty easy problem to solve or fix and when implementing captcha - just use your common sense and your own eyeball testing.



Is this going to be free Captcha or what ?

No financial expenditure needed here and I do not sell anything to do with captcha.
Only your own time, patience and perseverance will be needed.
And obviously your desire to combat spam.

The captcha solutions that I myself have learnt to implement are really easy and the main reason why I got into captcha was out of necessity to combat spam that my sites (about 60 of them ) were getting through the forms on them and since I absolutely hate spam and the spammers behind it, it is my pleasure to make their life more difficult if I can help other webmasters to implement captcha.
Also ... just by the by, I'm still waiting for my 15 minutes alla Andy Warhol and this is one small iota through which I have at least already had 3 minutes of your time.

Besides this, the main reason for this website was that myself being more of a programmer out of necessity than vocation, I found it hard to find really simple tutorials on captcha which show the less knowledgeable webmaster how to implement all the bits and pieces of captcha from a to z.

There are some great sites about captcha on the web but nine out of ten of them presume that the user has some basic knowledge of php, or of at least knowing how to include a .php document to the rest of the .html pages, or how to modify a few lines of PHP code and even how to combine the captcha image generation script, the captcha field and the captcha verification code all together.
Not an easy task if you are not versed in at least a little php, html scripting.

So if you read the few pages on this captcha website, you will be able to use some of the free captcha scripts downloads which are ready to use, and implement them, even if you only know how to use Dreamweaver, or FrontPage, and couldn't recognize a html tag if it hit you on the nose (more or less my case ).

[ If you are an expert captcha programmer - do me a favour and after you have read through these few pages, click the link above and read the page before you go and start breaking my b@!!$ about how little I know about captcha - I know next to nothing about captcha and that was the point of this whole captcha excercise so that I and millions of others could go and figure without a degree in php]


What does Captcha [ C.A.P.T.C.H.A ] stand for ?

Captcha stands for:
Turing test to tell
computers and

Which means more or less what it says.
A test, which should be passed by the human inserting a distorted code he sees in an image into a field.

The word Turing is the surname of Alan Turing, an english mathematical genius considered to be the father of computer science.

You will find links to the wikipedia captcha and Alan Turing pages on the captcha links page where you can read the facts about captcha and Alan Turing.


So - roll up your sleeves and here we go.....

Go to part 2 of 6 on understanding captcha:
Click on this link to continue your
crash course in captcha for beginners:



Site Index:

How to use the Captcha tutorials :

How best to use this captcha website - where should you start from ?


The six part captcha tutorial for beginners:

1 - How to use captcha - this page

2 - Forms without captcha   

3 - Forms using captcha.

4 - More examples of using captcha in forms 

5 - The captcha solution anyone can use on their website  

6 - Free Captcha download and implementation of captcha

6a - Captcha for the short sighted - implementation of large readable captcha


More advanced captcha tutorials:

How to insert captcha inside a web form

Captcha for more advanced web masters with some php know-how:

How to modify a captcha image

Online examples of Captcha:

Using captcha  

Another example of captcha   

Captcha within a web form

Very simple captcha    

Fully functional example of captcha and form

Captcha clock anyone ?

Large, BiG, GIANT Captcha, with captcha image tweaking options



Contact this website - if you have anything interesting to add

Other captcha information:

Captcha programmer

Captcha links to captcha resources


Captcha web site navigation

Captcha web site map

[ andare qui per tutorial su Captcha in italiano ]

Start date counter 22 - 08 - 2006