Locate an old pair of jeans with rear pockets in good condition. If you do not own a pair, visit your local thrift shop or ask a friend.
You are looking for a pocket that is large enough to fit your entire passport, make sure that it fits snuggly and is about a half an inch under the opening of the pocket so that it won't fall out easily.
Remove the pocket from the jeans with a pair of scissors, being careful not to cut any holes into the pocket itself.
Locate a zipper that is about the width of your pocket and securely attach it to the opening with a sewing kit.
Locate a strong but comfortable material which will go around your neck such as a lanyard and attach it securely to the pocket.