Client-side CAPTCHA ceremony for user verification

A facility for performing a local human verification ceremony to obtain user verification is provided. Upon determining that user verification is needed to perform an action on a computer system, the facility presents a CAPTCHA challenge requesting verification that the user wants the action performed on the computer system. Upon receiving a response, the facility compares the received response to an expected correct response. If the received response is the correct response, the facility authorizes the action to be performed.