BACKGROUND ART
An image display device that is mounted on the head or the face to be used for viewing an image, that is, a head-mounted display is known. The head-mounted display includes an image display unit for each of left and right eyes, for example, and may enable a user to observe a realistic image by forming an enlarged virtual image of a display image by a virtual image optical system. The head-mounted display is highly popular. If mass-produced in the future, the head-mounted display may become widespread like mobile phones, smartphones and portable game consoles, and it is conceivable that every person will own one head-mounted display.
The head-mounted display is equipped with a high-resolution display panel of liquid crystal or an organic electro-luminescence (EL) element, for example, as a display unit for left/right eye. Also, the head-mounted display may be categorized as a transmissive type or an opaque type.
A transmissive head-mounted display enables a wearer to observe the surrounding scene, while mounted on the head and displaying an image (for example, see Patent Document 1), and thus, the user may avoid dangers of running into obstacles and the like at the time of use outdoors or of use during walking.
On the other hand, an opaque head-mounted display directly covers the eyes of a wearer when mounted on the head, and the sense of immersion at the time of viewing an image is increased. By enlarging and projecting a display image by using a virtual image optical system, and enabling a user to observe an enlarged virtual image with an appropriate angle of view, and also, by reproducing multichannel sound by headphones, a realistic feeling of viewing in a movie theater may be recreated (for example, see Patent Document 2). Furthermore, also with the opaque head-mounted display, there is known a video see-through method according to which a camera for capturing the front of a wearer is built in and an external image obtained by capturing is displayed, and the wearer is enabled to observe the surrounding scene through the external image (for example, see Patent Documents 3 and 4). Additionally, in contrast to video see-through, the term "optical see-through", or simply "see-through", is used for the aforementioned transmissive head-mounted display.
Now, with information appliances such as multifunctional terminals, such as mobile phones, smartphones and tablets, and personal computers, whose users are limited to individuals or specific user groups, input of a passcode or a password, or an authentication process using biometric information or the like is generally performed at the time of start of use.
For example, there is proposed an electronic appliance which is provided with a touch panel display of a depression amount detection type which displays a user authentication screen for an authentication required function, checks input number information indicating a plurality of different numbers input by a user on the user authentication screen against passcode information that is stored, and releases the lock on the authentication required function in the case of match (for example, see Patent Document 5).
Also with the head-mounted display, if users are limited, such as in the case of personal use, an authentication process has to be performed at the time of start of use.
For example, there is proposed a glass-type or head-mounted image display device which allows display of an image on a display on the condition that biometric authentication, such as iris recognition, retina recognition, face morphing (morphing) or skeleton recognition, has been performed (for example, see Patent Document 6).
Furthermore, there is proposed a head-mounted display which performs user identification or an authentication process by detecting movement of the gaze position or gaze point of a user by using a myoelectric sensor or an electrooculogram sensor for detecting a muscle potential or an eye potential, and by using a movement pattern of movement of the gaze position or the gaze point of the user (for example, see Patent Document 7).
Generally, with a system which is set with an authentication function, an authentication screen is displayed at the time of start of use, and a normal operation screen is not displayed until the authentication process has been performed.
In the case of the opaque head-mounted display, both eyes of the user are covered, and the user is placed in a state of being blindfolded with no view. If a built-in camera is turned on and a captured image is in the manner of video see-through, the user regains view, and may observe the surrounding scene. However, if the authentication function is set, a video see-through image cannot be observed until the authentication process is performed, and a state of blindfold is kept. If the authentication process is disrupted by erroneous input of a password, for example, the user is placed in a dangerous state because the view becomes lost for a long time.
