CAPTCHA

A CAPTCHA is a challenge-response test used to distinguish likely human interaction from automated or abusive traffic. It may ask a visitor to recognize images, enter text, solve a simple interaction, or pass a risk check that requires little visible action.

Sites can present a CAPTCHA after signals such as a poor IP reputation, a sudden request spike, repeated failed logins, missing browser features, unusual navigation, or a mismatch between headers and browser behavior. The challenge is often one step in a broader risk system rather than proof that the visitor is a bot. Shared proxy and carrier addresses can also accumulate signals from unrelated users.

For legitimate automation, the right response is to reduce the triggers rather than attempt to break or outsource the challenge. Slow the request rate, use backoff, preserve session state, correct malformed requests, and stop if the site indicates that automated access is not allowed. Repeatedly retrying a challenged request can increase the risk score and affect more addresses.

The troubleshooting guide fix common residential proxy errors covers response checks and recovery steps.

Related terms: rate limiting and browser fingerprinting.