The law in Florida is that non-US residents (it may even cover anyone out-of-state) have to show a passport for ID for alcohol and the law also states that they are also supposed to ID everyone. There used to be signs at WDW stating that they would card you if you looked under 30 but I now see signs everywhere indicating that you must provide passport as ID if you are from out of the country - no exceptions noted. Ostensibly the reason they need a passport for non-residents is because they don't know what driver's licenses or other government ID look like from out of the country, so they have no way of knowing if it is a forgery. Nowhere does it indicate that they will accept a photo or copy of the passport.
However checking everyone's ID just doesn't seem to happen in practice unless the establishment has reason to believe that they are being scrutinized or they recently got in trouble. There have, however, been a number of people on these boards who have indicated that they had to show both passport photo on their phone in addition to other ID and many have indicated that they are young or look young. Personally, I have not been carded at WDW for many many years. They may be still using the "you look under 30" rule of thumb to keep service moving efficiently (I absolutely don't look under 30) but it's a totally unofficial operational rule so I still bring a copy of my passport on my phone and always have my driver's license with me in case.
