Its known as the Disney Photopass. There are official Disney photographers at the 4 parks. On your first day approach one of these and they will take your photo then issue you with a credit sized Photopass Card. Each time you see an official photographer show them this card, they will take your photo and then scan the card.
Photos can either be picked up already processed at the photoshops in the parks (at approx $16 each). Or you can wait until you get home and go on line and buy them from there, or at the end of your holiday you can get at CD burnt. This will cost $100 plus tax, so if you've had a load of photos taken its well worth it.
The CM will also put on all the signatures and borders on for you. Your disc will have two folders: one with your original photos and one with the enhanced photos.
You can then print them off at home or go to the local photobooth to have them printed.