Which system consists of a publicly available set of databases that contain domain name registration contact information?

WHOIS is a query and response protocol used to query databases that store the registered users or assignees of an Internet resource, such as a domain name, an IP address block, or an autonomous system, making this information publicly accessible.

CAPTCHA (Completely Automated Public Turing test to tell Computers and Humans Apart) is a security measure to distinguish human users from bots, not a database of domain registration information.

IANA (Internet Assigned Numbers Authority) is responsible for global coordination of IP addressing, DNS root zone management, and other Internet protocol resources, but it doesn't itself host the public WHOIS database.

IETF (Internet Engineering Task Force) is a community that develops and promotes Internet standards, but it is not a database system for domain registration information.