CAPTCHAtyyppejä

CAPTCHAtyyppejä, short for Completely Automated Public Turing test to tell Computers and Humans Apart, are security measures designed to distinguish between human users and automated bots. Their primary purpose is to prevent malicious bots from performing actions like spamming, credential stuffing, or scraping websites. Various types of CAPTCHAs exist, each with its own approach to verifying human interaction.

Text-based CAPTCHAs are among the oldest and most common. These typically present distorted or obscured letters and numbers that users must decipher and type into a text box. The distortion aims to make it difficult for optical character recognition (OCR) software used by bots to read the text. However, advanced OCR technology has made these less effective over time.

Image-based CAPTCHAs require users to identify specific objects or patterns within a set of images. For instance, a user might be asked to select all images containing a traffic light or a bicycle. These rely on a human's ability to interpret visual cues, which is generally harder for bots to replicate accurately.

Audio CAPTCHAs are an accessibility alternative for visually impaired users. They present spoken letters or numbers that the user must transcribe. Similar to text CAPTCHAs, the audio is often distorted to impede automated speech recognition.

More recent developments include behavioral CAPTCHAs, like Google's reCAPTCHA. These systems analyze user behavior in the background, observing mouse movements, typing patterns, and interaction timings. If the behavior appears human-like, the user may not need to solve a visible challenge. If suspicious, a traditional challenge might be presented. Other variations include simple checkbox CAPTCHAs ("I'm not a robot") that trigger background analysis, or mathematical problems that are easy for humans but more complex for simple bots.