What is captcha and when to use it?

CAPTCHA is an acronym for Completely Automated Public Turing test to tell Computers and Humans Apart. As you can guess captcha is a kind of test. It is used to recognise whether a certain act performed on a computer is done from a real user or by a program/code/script. Captcha is mostly used on web sites to track real users and limit harmful activities from unwanted software.

In it’s basic form captcha is a field consisting of images with distorted words or a row of numbers. It could be an image of street name or house number. Due to the many font combinations, shooting angles, colours, lighting and other factors, a software would hardly recognise the content on all pictures. So this is a great way to differentiate between computer and user activity.


Most often you would see captcha under contact forms. It is place there, because there are scripts that could harm the files of your web site through your contact form.

Another example is placing captcha when a user writes a comment on a blog. This is done to avoid SPAM comments and jamming up the comment section in the administrative panel.

What could captcha prevent?

With captcha you can prevent the acts for a script, which:

  • can create multiple ghost registrations on your web site. This would lead to false statistic of users and user visits. Furthermore this would also lead to expenses and loses for server space for these registration.
  • aims at sending SPAM messages to your organisation. This could jam your inbox with unwanted messages. As a result you may have to stop your work until all the SPAM messages are deleted and you free some space to receive new messages. Depending on the intensity of the messages, this could possibly lead to you missing on an important message from a customer, since you spent all your server space on SPAM messages.

Placing a captcha of your web site

There are multiple free captcha codes you can implement on your web site. However you could ask your programmers to build you one, if you do not feel the available ones are secure enough.

Still do not place captcha on every step/page of your site, because this may irritate your real users. You could place it on the first and last step of a certain process, before sending the actual data to the database.