In operation 1510, the wearable device 100 may register execution authority of a user and a vein image of the user. The wearable device 100 may register a function or an application available to each user. In other words, the wearable device 100 may register execution authority of each function and each application for each user. For example, the wearable device 100 may store that a first user has authority to execute a function C and an application A, and a second user has authority to execute a function A, a function B, and an application B. Multiple functions and applications may be available to a particular user, just as multiple users may have authority to access a particular function or application.

In operation 1520, when the function or the application is selected, the wearable device 100 may capture a vein image of the user wearing the wearable device 100.

In operation 1530, the wearable device 100 may identify the user wearing the wearable device 100 by comparing the captured vein image with the registered vein images.

In operation 1540, if the identified user has the execution authority, the wearable device 100 may execute the function or the application. For example, when the first user wears the wearable device 100 and the application C is executed, the wearable device 100 may determine whether the first user has the authority to execute the application C, and the wearable device 100 may execute the application C only when the first user has the authority to execute the application C. When the first user no authority to execute the application C, the wearable device 100 may provide feedback to the user indicating that the application C may not be executed because he does not have the authority.