Same way.
There's the account online, and there's the card. Totally separate until you get home and enter the card number(s) onto the account.
You can have a gazillion cards if you want to...sometimes hubby goes off one way and I go the other (DS usually goes with hubby!) so we make sure we have two cards. If there were other friends or family with us, each group or even each person could have their own card just in case they get the urge to have their pic snapped.
Then at the end all those cards (or rather the numbers on the backs of the cards) get entered onto your online photopass account, and that's how the pictures get on the account! It's like magic.
Unless something goofy happens (ha ha), then it's a little less magical, but after a little back and forth via email I finally got my points and requests across, and then it was truly like magic.
Jenn, if you're thinking of the Tinkerbell floating above putting dust down, that's a border that you can edit onto any of the pictures. Though I do find that if a kiddo is in a stroller, those pictures don't work, b/c the words at the bottom cover up the kid.
The special picture that can be taken puts Tinkerbell in your hand outside the castle. You pose, pretending Tink is in your hand (or your DD's hand), and the photographer works some magic and it *should* end up in that picture. As we've seen, sometimes there are issues with that actually happening! But now you know that it *can* be remedied, if tink doesn't show up (i can't even tell you how stupid our DCA Stitch-popping-out-of-ground pictures looked when Stitch was not actually there...even once the nice email photopass people added him, I'm pointing one way and looking just slightly the other way, and DS isn't looking there at all, so it's still silly. I think Tink would be easier).