tink3kids is correct that you will need to go to the ticket booth to process your AP on the day of first use. However, if you wish, you can actually enter the park first using your printed vouchers at the gate. You will be issued a temporary paper ticket which you will need to turn in at the ticket booth before park closing that day to swap out for your proper AP. That process will take at least a few minutes. Then you will still have to go get the photo taken inside one of the parks, and that too can take a few minutes. We have occasionally encountered no wait at the Buena Vista photo shop, so that's another location to consider for the picture-taking. Disney wants you to get your picture taken ASAP, and you will have to show your picture ID each time you enter the park until your picture gets added to your record. That said, you are still ok if you don't manage to get your photo done that first day; just do it the next day that you enter the park. You MUST get the actual AP processing done though on the first day of use.