All of the roving photographers in the parks are now PhotoPass photographers.
PhotoPass photographers take your picture, just like the roving photographers have always done, only now instead of getting a slip of paper to claim your photo later, you get a PhotoPass card.
Once you have a PhotoPass card, you hand it over to any PhotoPass photographer who takes your pic anywhere at WDW; the photographer swipes your card on a piece of gear connected to their camera, and Bingo! The pics are associated with that card.
Either at home, or at the camera shops in the parks, you use the card to view your pics and buy those you want. You can have multiple cards, so don't worry if you leave one in your room (many people like to get a new card each day in case they lose one, that way you only lose one day of pics).
If you have a lot of pics, you can buy a CD at the camera shop before you go home for $100 with all of the pics on it in hi-res format; then you can print the ones you want at home or at a pro printing place like Shutterfly or DotPhoto.
PhotoPass photographers can be found at the entrances to each park, at certain photo spots like the Partners statue, the Fountain of Nations, and the BAH, and at a few other miscellaneous places.
Ride photos are not part of the PhotoPass system, so if you want to buy them, you have to do it on the spot, as always.