Some of the people on these boards are so creative they have designed pages that you can print out with the character on it and they suggest getting it bound at Staples in a loop binder for around $4.
Mine was easier for me because I am not computer literate. I made them for my neice and nephew when we went a few years ago.
I bought a small 4X6 photo album at AC Moore for $1. I then got 4X6 unlined index cards for the book.
There is a list on one of the boards, (maybe someone else can send the link), of all the characters who are in the parks and where you can find them.
I went through quite a few pages of Disney clipart and printed out pages of characters about 2" tall and cut them out and glued them on the index cards. If you are more computer able maybe you can print them directly on the cards.
When we saw a character the kids just got into line, pulled the card out of their book and had the character sign it. The characters seem to get more excited when they see a photo of themselves and pantamine that it is them. The kids loved that.
When we got home my SIL took the cards out of the albulm and put them into a bigger albulm with the photos of the kids with the character. We did this 4 years ago and they still look at the book today.