Public certificates can be viewed by anyone who has access to the URL link.
Information such as the owner of the artwork is not available on any Verisart certificate. The identity is represented on the certificate by a 'Public Owner Key'. Copying this key does not give anyone access to your certificate details on the blockchain.
Private certificates require approval to be viewed. As the viewer, you can request access to the certificate. The owner will receive an email notifying them that someone has requested access to their certificate. The owner can then choose whether they are happy to share the certificate, either by sending the pdf or by making it public. The private view is only available to Premium and Business Plan users.