Image display device, image display system, and method of controlling image display device

A method of controlling an image display device, the method comprising:

• providing the image display device having
• a clock section adapted to time current date/time information including a date and a time,
• an expiration date/time storage section adapted to store expiration date/time information as information of a date/time until which use of the image display device is allowed, and
• a unique number storage section adapted to store a unique number of the image display device, and
• adapted to display an image;
• accepting input of a password encoded based on the information of the unique number of the image display device and the predetermined expiration date/time information;
• decoding the predetermined expiration date/time information from information of the password accepted in the accepting;
• comparing the predetermined expiration date/time information decoded in the decoding and the current date/time information timed by the clock section with each other;
• and
• storing the predetermined expiration date/time information in the expiration date/time storage section if the predetermined expiration date/time information decoded is a date/time one of on and later than the current date/time information.