Some games, especially early computer games used forms of copy protection that needed some sort of physical object. Some times this required users to look up a specific word in the manual, use a form of wheel that would reveal a word, or even a dongle that users had to plug in.
One of the earliest types of physical copy protection involved the users having to find a specific word on a certain page and line of the game's manual. This form of copy protection would also on occasion be needed during gameplay, such as creating potions in King's Quest III.
To combat the easy photocopying of these pages, some games started coming with a specific manual or slip of paper that had darker colored paper to make it not show up when photocopying.
Code wheels are multiple pieces of circular card stock or paper of varying sizes that were overlayed on top of one another. There were often holes cut out in the middle that would reveal a word, phrase, or image based on what was lined up on the outside edges.
Some games, such as DJMAX Trilogy used a physical dongle that must be plugged in for the game to function. Most use cases for a dongle or physical key were used in arcade cabinets to try and curb bootlegs.