What is a CAPTCHA?
A challenge-response test designed to distinguish humans from bots, usually presented as image, audio, or behavioral puzzles.
Also known as: reCAPTCHA, human verification
CAPTCHA stands for "Completely Automated Public Turing test to tell Computers and Humans Apart." It dates back to 2003 and originally meant distorted-text puzzles. Today the field is dominated by Google's reCAPTCHA v3 and Cloudflare Turnstile, which run silently in the background and score user behavior instead of showing a puzzle most of the time.
CAPTCHAs exist to stop automated abuse: scraping, credential stuffing, fake account creation, comment spam. They work by exploiting tasks that are still hard for bots (image classification, mouse-movement patterns, browser-fingerprint consistency) even after a decade of rapid ML progress.
For scrapers, CAPTCHAs are an obstacle. The honest workaround is to use the site's public API or buy data through a partnership. The technical workarounds (captcha-solving services, residential proxies, fingerprint randomization) work but get more expensive every year as detection tightens.
In the wild
- hCaptcha image-grid challenges ("select all squares with a bus")
- reCAPTCHA v3 returning a 0–1 risk score with no user interaction
- Cloudflare Turnstile running invisibly until risk exceeds a threshold