GlossaryAnti-BotBeginner

CAPTCHA

A CAPTCHA is a challenge–response test used to tell humans and bots apart, such as identifying images or checking a box, to block automated access.

Last updated May 28, 2026

Definition

A CAPTCHA (Completely Automated Public Turing test to tell Computers and Humans Apart) is a challenge designed to be easy for people but hard for bots. Common forms include distorted text, image-selection grids, and invisible scoring systems like reCAPTCHA v3 that judge behavior without any visible puzzle.

Why sites use CAPTCHAs

They throttle automated abuse — scraping, credential stuffing, spam and fake sign-ups. For automation projects, CAPTCHAs are a primary obstacle, handled by reducing bot-like signals (good proxies, realistic fingerprints) or by using solving services.

Examples

1

A reCAPTCHA image grid asking you to select all squares with traffic lights

2

An invisible reCAPTCHA v3 score that silently flags suspicious sessions

Common Use Cases

Blocking automated bot traffic
Preventing spam and fake account creation
Mitigating credential-stuffing attacks
Rate-limiting abusive scrapers

Frequently Asked Questions

They minimize bot-like signals using residential or mobile proxies and realistic browser fingerprints, and when a challenge still appears they may use a CAPTCHA-solving service.
High request rates, datacenter IPs, suspicious fingerprints, and unusual behavior patterns all raise a site's risk score and can trigger a challenge.

Keep Learning

All terms

Browser Fingerprinting

Browser fingerprinting identifies and tracks a device by combining dozens of browser and system attributes — like fonts, canvas rendering and user agent — into a near-unique signature.

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Rate Limiting

Rate limiting restricts how many requests a client can make in a given time, and it is one of the most common defenses scrapers must work around.

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Anti-Detect Browser

An anti-detect browser lets you run many isolated browser profiles, each with its own fingerprint, cookies and proxy, so sites see them as separate, genuine users.

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Web Scraping

Web scraping is the automated extraction of data from websites — fetching pages programmatically and parsing their content into structured data.

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