An image processing apparatus capable of an authentication technique which enables appropriate user authentication on an application-by-application basic without requiring users to perform time-consuming operations. A storage unit stores authentication method setting information in which authentication methods for respective ones of a plurality of applications are set. An authentication method determination unit determines an authentication method for use in authentication to be performed before a selected application is executed, based on the authentication method setting information. An authentication unit performs the authentication using the authentication method determined by the authentication method determination unit. The authentication methods include at least a first authentication method that does not require input of authentication information and a second authentication method that requires input of the authentication information.