Photopass is a service (free to use, you pay to buy the photos or the CD)
Disney photographers are stationed around all of the parks and waterparks, usually at icon locations (Main street near the castle, epcot in front of Spaceship Earth, DHS on sunset boulevard and near the sorcerer's hat, AK near the tree of life, to name a few), as well as at the character meet & greets. You get a card (credit-card sized- that the photographer will scan, and then take your photo.
After your trip (or during, if you're impatient) you can get on the website, enter the number from your card or cards (you can have more than one) to browse the photos, make photo books, order prints, or order your CD.
You can also ask the photographer to take a picture with your own camera at no cost. They're more than happy to oblige!