Originally posted by XStAnt
Although I'm not an expert on this I believe each ticket has a unique serial number printed on the back (and probably also coded on the magnetic strip).
If you lose your ticket but photo copied the back Disney can enter the serial number, see if it's been used and/or # of days remaining, deactivate that ticket (so no one else can use it), and issue you a new ticket with the correct number of days remainig, etc.
Without that info Disney would have no way of verifying how many days were left on your ticket or deactivating your ticket. They would have no way of knowing if you truly lost your ticket or were just claiming it was lost in order to get a free ticket.