There are photographers throughout all the parks, including the water parks. Just hand them you're card, and they'll add the pictures to it. You can find them infront of the main Icon, with most of the characters, and some of the smaller "icons", such as Tower of Terror, Everest, Rockin, Nemo. Some of them are set up for particular "magic" shots, like in front of Pirates, Soarin, or Haunted Mansion (usually only during halloween time though). These photos are edited to create a special surprise. Almost all photographers at icon locations can take a magic shot.
You'll get about 3 photos each time you have your picture taken in front of an icon. And about 5 photos when you see a character. Although night time photos at icon, it's only 2.
Occasionally, you can get more photos added. Like if you participate in the Tiana Showboat Jubilee (dunno if that's still going on though), or if you're the grand marshals of the Parade. Or if you're the lucky Veterans of the Day, and help take down the Flag on Main Street (everyday at 5pm).
They also take pictures of the marching bands that participate in the Magic Music Days.
Throughout the Deluxe resorts, you'll occasionally find a photographer roaming the lobby.
All of these photos can be added to your photopass card. And don't worry about multiple cards, you can register more than one to your account. Just make sure to take a picture of the back of the card with your own camera, or some how save the number on the back of the card. You don't need the physical card to pull up your pictures, you just need that number. So in case you loose it, you won't have to go through trying to find your photos. And in the parks, it takes two seconds at the Camera store for a CM to type in your old card number, and put all your photos on a new card.
Now at certain dining locations, they will take a picture of your group prior to seating. And while you're eating, you will be shown the photo and offered to purchase it for 30$ (you must purchase it, to have the photos added to your photopass card). It's one 6x8 and four 4x6 photos, in a cute little folder resembing the location you're at. The current dining locations are Chef Mickeys, Ohana's Breakfast, Luau, Hoop-de-doo review, Tusker House, Norway princess, and 1900 park fare. Cinderella's Royal Table is the only location that includes the pictures with the dining. They also take pictures at the "my perfect tea party" at the Grand, but I think those photos are just added to your card, not 100% sure.
There are also photographers located at the Pirates League and BBBoutique. If you do the highest package, photos are included with it. Lesser packages, photos are just added to your card.