Ads Captcha

Captcha is known for being a spam prevention effective solution in regards to all forms of spam that can be done by bots. The reason for that lies in the fact that Captcha is a test that validates web users as human beings, just as the name implies: CAPTCHA = Completely Automated Public Turing test to tell Computers and Humans Apart.

What form of spam Captcha can prevent then?

Among others, Captcha is able to prevent forum spam, comment spam or spam in blogs, guestbook spamming and newsgroup spam.

Forum spam – What, How and Why?

Forum spam is a process of posting abusive advertisements or unwanted messages on internal forums, generally by spam-bots. It is done by inserting a link or dozens of links into the forums. The links come with minimum text and the content is mostly irrelevant to the forum but still it is inserted in hope that it will prevent spam filters from carrying out their mission. By adding links to the forum, the spammer strive to attract potential customers to its site.

Comment spam / Spam in blogs

Similar to forum spam, links that point to the spammer’s website are inserted into blogs using the section of comments given by the blog.

The one who is behind these comments spam is doing it in order to increase his site search ranking! Inserting as many links as possible, while using keywords as anchors, also increases the number of potential visitors or paying customers to the spammer’s site.

Guestbook spamming

According to Wikipedia, a guestbook is “a paper or electronic means for visitors to acknowledge their visitation to a site, physical or web-based, and leave their name, postal or electronic address (if desired), and a comment or note, if desired. It is used at museums, hotels, churches and so on”.

This applies to the web as well.
Web sites use guestbooks to display the type of visitors who visit the site as well as getting a feedback from the visitors about the site. (The visitor is not required to open an account and can leave a public comment).

Commercial website spammers may leave endless comments adding links to their site for the same reason mentioned before – increasing the number of potential visitors or paying customers to the spammer’s site.

Newsgroup spam

Newsgroup spam is a process of posting endless articles with faked and falsified article headers to usenet newsgroup in order to disrupt and make the newsgroup unreadable.

Can we fight against those forms of spam?
Yes. We can!

Since captcha demands the user to prove he’s a human being (by solving a simple test that humans complete easily) bots that run into the captcha test while trying to sign them selves up to all kinds of online platforms such as forums, guestbooks or blogs – are being stopped simply because they can not complete the test.
In other words -
Captcha is the perfect solution for online spam prevention!

Captcha is a test that comes to validate web users as humans (=rather than computer bots).
the captcha test can be used for site registration, for example – just before registration is completed the user is asked to copy an  image with distorted letters. Since those letters are captured in images and are displayed randomly, and bots can not “read” images, the CAPTCHA test suppose to “stop bots from passing the test and using the web for their inetrests”.

But what about people who suffer from some kind of sight impairment including blindness?
They can not solve the captcha test (they can not see the captcha image well and thus can not copy it) and thus, just like bots, can not register to sites and other online services that use captcha.
But do not worry, there’s a solution for this problem and it called: Audio Captcha.

People who suffer from sight impairment need to pass an audio captcha test in which they are asked to listen to a series of numbers or letters with a lot of background noise and then repeat them through typing the letters/numbers.
The idea is that humans can filter the background noise but a computer bot – can’t.

Unfortunately the audio captcha test is not perfect.
First, there are people who suffer from sight impairment / blindness that also have hearing problems.
Second, statistic shows that only 46% of audio captchas users are able to decipher the test and that the process takes 65 seconds at least , relatively much longer than a textual Captcha (about 12 seconds).
Third, most of the sites don’t use audio-captchas yet.

What other transformations will make the captcha test suitable for all?
Only time will tell…

Captcha is known for its efficiency in ensuring proper use of websites and online application by validating that the user is human and not a bot or some other automatic machine.
This article lists some of the security applications / uses of CAPTCHA:

Comments spam prevention

Comments spam is used in blogs and forums mostly for raising search engine ranking of websites. A “spammer” who wants to get some free traffic to his website might get into a variety of blogs or forums and add comments with textual (using keywords as the anchor) links leading to his website.
The advantage of using captcha in blogs and forums adding comments option is that it can block automatic machines that can do this kind of spamming. Bots don’t know how to read captcha and thus cannot pass it.

Online Surveys and Polls

When you want to trust the results of an online poll and be sure that only human votes are counted – use Captcha. This way you’ll ensure that only human will take a part in the poll and at the same time prevent the possibility of biased results (by bots).

Spam blockers / Protecting Email Addresses from spam scrapers

Captcha is also known as a great spam blocker against spammers who search the web for e-mail addresses. You want to allow your users to send you emails but don’t want to get spammed by bots? All you have to do is to ask your website visitors to solve a confusing Captcha before you show your e-mail.
Just the same, the CAPTCHA test can be used to protect from massive registration to free email accounts.

Search Engine Bots

Have some confidential pages on your website that you don’t want the search engine bots to reveal (and index)? Use Captcha to prevent all kinds of bots, including those of the search engines, to get to them.

Free anti spam

Lots of companies wish to accept mails only when they are 100% sure that the e-mail sender is not an automated machine. One of the easiest ways to get this is by using Captcha as a spam filter.

Captcha protects your website from unwanted users such as automated machines, bots and spammers. Once you have decided to use Captcha for your site, there are some important criterions you must take into consideration:

Accessibility
Captcha must be accessible for every user – for the normal and the blinds.
That means that the captcha image shouldn’t be too small and it should offer an alternative (audio one for example) for the ones who can’t see well or don’t see at all.

Image security / complexity
Captcha images should not be easy to percept.
They should be vague and distorted so no bot can solve it – only humans.

Script security
A Captcha code should consist of images that are not readable by bots as well as questions that can be answered only by using human intelligence.

Security of CAPTCHA wide spread use

When Captcha system is adopted by a great number of sites it could weaken its security effect, since a parser could make it easy for bots to solve the Captcha test. Since it is highly important that Captcha will be of strong security even when it is widely used, it is recommended to use well-tested implementations of *reCAPTCHA than to create your own CAPTCHA script.

* reCAPTCHA is a free service that helps to digitize old media such as books, newspapers and radio shows so they can be used as CAPTCHAs