What is CAPTCHA?
CAPTCHA is a part of every internet user's daily life. We are asked to complete CAPTCHA tests when creating accounts, logging into services, and posting comments. Even though they can be annoying at times, they play a significant role in online security. How do CAPTCHAs work, are they necessary, and can they be unsafe? Read on to find out.
A little history
CAPTCHA, which stands for "Completely Automated Public Turing test to tell Computers and Humans Apart," is a security measure used to verify that a user is not a bot trying to access a site. The idea for the test was first created by Alan Turing, a mathematician and an important figure in computer science. The Turing Test, which he proposed in the 1950s, is one of the earliest and key contributions to the development of artificial intelligence. The initial test involved a human evaluator communicating with an entity they couldn't see—either a human or a machine—through text. If the evaluator couldn't distinguish between the machine and the human, the machine was considered to have passed the test. Modern-day CAPTCHAs are much more complex but are based on this original idea.
Types of CAPTCHAs
There are three main types of CAPTCHAs: text-based, image-based, and audio. Let's take a closer look at each type.
Text-based
These CAPTCHAs show users distorted text containing a random set of letters, numbers, or quotes. Such tests are considered traditional CAPTCHAs because they appeared before other variations. The key here is that all elements are heavily distorted—blurred, stretched, or narrowed, twisted, overlapped with additional symbols. This makes reading the text difficult for machines and sometimes even requires a human to guess a few variants to correctly decipher the original text.
Image-based
In this case, the user must interpret, recognize, and correctly identify not text but an image. The images can be anything—photos, graphic elements, or hand drawings. Most often, the task is to select all images related to a given theme, for example, all cars. In practice, image CAPTCHAs are the easiest and simplest to understand, though mistakes can still occur due to inattention.
Audio
This variation is most often used by people with visual impairments. The system plays an audio file that needs to be understood and entered for confirmation. The sound is usually distorted or contains background noise, making it more challenging for bots.
How do CAPTCHAs work?
CAPTCHA presents the user with a test that must be completed to continue the desired action—be it accessing a website or opening a specific web page. You won't be able to proceed without providing the correct answer, but if you fail at the first attempt, you can always request a different test or change its type. As mentioned above, the image-based test shows users several pictures, and most often, users need to select those that match or don't match a theme. Text-based CAPTCHAs are more traditional, displaying a distorted string of letters or numbers for the user to type into a box. After the test is completed, the system recognizes that the user is human and allows them to continue what they were doing on the web page.
Can CAPTCHAs effectively stop malicious bots?
While CAPTCHAs help prevent attacks by malicious bots, they are not foolproof. Although these tests are useful for identifying and filtering out bots, cybercriminals can find ways to manipulate and bypass them. Nevertheless, CAPTCHAs continue to contribute to making accounts and websites safer for users. The complexity of CAPTCHAs makes it more difficult and time-consuming for cybercriminals to carry out attacks. As a result, they require more resources and time to successfully launch an attack, which may deter some of them from targeting a CAPTCHA-protected website.
