If you have a voucher of some sort, you take your lovely little voucher to the ticket booth and they exchange your voucher for little cardboard-y pieces of paper that you can use to get into DL or DCA, and you can use them in the FP machines.
When the line at the Bank is short or you are ready - you take your little cardboard-y pieces of paper and stand in line and get your picture taken. Everyone in your family who has an AP will have to have their picture taken. It was actually pretty quick for us when we had it done in May. I love to see my youngest's picture and he loves to hold his AP and look at his own picture, too.
When you go to enter one of the parks your picture will pop up and they can compare what you look like - so they know it's you.
I saw some girls who looked like they were cheating the system when we first used our passes - one girl's pass had her picture on it and I am pretty sure the other girl was using the first girl's younger sister's pass, because the CM at the turnstile called a Lead and had to get special permission to let her in. They just told the Lead that she hadn't had her picture taken in a long time - or she had had an AP for a really long time and just hadn't updated her picture. Seemed kinda scammy to me.