CAPTCHA

A challenge a website shows to tell humans from automated programs, such as picking images or ticking a box.

Last updated September 28, 2026.

Definition

What CAPTCHA means

CAPTCHA stands for Completely Automated Public Turing test to tell Computers and Humans Apart. Sites show one when traffic looks automated: too many requests from one address, a browser that behaves oddly, or an address with a bad reputation. Modern versions often run invisibly and score the visitor instead of showing a puzzle.

For scrapers a CAPTCHA is a failed request. Avoiding them, by pacing requests, using good proxies, and behaving like a real browser, is cheaper than solving them.

When a source blocks a Clair request, Clair retries it by another route. If every route fails, the request ends with a 5xx error and is refunded.

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