Remote Secure Shell servers are authenticated by a public-key procedure. The user checks the fingerprint of the remote server's public key. When the user has approved the public key, it is stored in the user's $HOME/.ssh2/hostkeys directory and will be used automatically thereafter.
The verification step requires user interaction, so even for users that are set up to run client programs unattended, the first connection must be done by a person who logs in as the user, accesses the remote server, and goes through the fingerprint check dialog. The same steps must be repeated if the remote host's key is changed.