Photopass is a great offer by Disney. At each park, they have their photographers stationed near the main icons (Cindy's castle at the MK, Spaceship Earth at Epcot, Tree of Life at AK, etc.). They will take your photograph. They are also sometimes stationed in the character greeting areas, and will take your picture posing with the characters.
The very first one you meet will give you a card with a magnetic strip. From then on, whenever you have one of Disney's photographers take your picture, you hand them your card and they "swipe" it. Don't lose your card!!
When you get home from Disney World, you log onto the Photopass website and enter the code on your card. All of the pictures that they took of you will be on the website. You then have 30 days to decide if you want to purchase them or not. You can buy 1 photo, multiple photos, or all of them! You can have graphics put on them, or not. You pick the ones you want!
We always have the photographers take our family pictures at each park. When we return home, we pick the best 1 or 2 and have them printed and mailed to us.
ONE other thing to note... and this is a freebie! The Disney photographers will also take a picture of you/ your family with YOUR camera in front of the icons for free! So, we always have their photog take our picture with our camera, and then take several with theirs. Theirs are always better, so we end up buying one or two, but we also have all of ours that were free!
It can also be handy on the days when you just don't want to carry your camera around. They can take your picture with Mickey, and you don't have to have your camera!
Hope this makes sense. Please feel free to ask any other questions, and I'll do my best to help.