Not so fast. What if they have only seen the movies? Then heck, they won't know a whole lot about Nymphadora Tonks, now will they? It is right to assume someone who wants to play such a game will have a passing knowledge of the universe in question, but they will want to know, they may even need to know, more background (It may be prudent to give out spoiler warnings to players if they have not read or seen all the source material). Web sites like Wikipedia are ideal starting points for this information, but there are plenty of others. For example, if you are running a Star Trek game ditl.org has everything you could possibly need regarding ships and canon characters.
So, this just sounds like more NPC stuff, right? And this is true, a large part of your world's background does involve that characters that populate it. So let's move on. What else do you need? What about the home where your characters live, or the base they are operating from? Or the ship they fly through space in? What about the city where the campaign takes place? What do your players know about it?
World building is very important and as the GM you must provide plenty of detail to give it life. If it takes place mostly in one city or community, be it fictional or real, they need to have some idea what the place is like. Give them descriptions of the neighborhoods, a history of the city, background information about important historical figures that may have had an impact.
In Star Trek this is especially important. One of the criteria many players use to determine whether or not they join a game is based on what sort of ship is being used. Choice of a weaker science vessel implies your game will be more inclined to have games involving exploration themes, while using something more combat oriented would suggest your game will have more action. Prospective players need to know this up front.
Which leads me to the next item concerning world building; images. Fair use laws are pretty complicated (at least they are to me) so please do not take anything I say as absolute fact. The biggest issue regarding use of images found on the internet concerns profit; at FedEx Office, for example, we are not allowed to make duplicates of pictures found on the internet because that would mean we are profiting from it. Provided 1) your images copied are for private use, 2) not for profit and 3) you are not claiming to be the owner or creator of said images, then I believe you should be all right to use them for your game. If the owner does object, however, then it is imperative that you accede to their wishes and remove it. It is important to note copyrights; when I ran my Star Trek game I gave credit to Paramount.
I have used images of celebrities to portray characters, floor plans of mansions for bases, maps of cities to show the campaign city. And where Star Trek is concerned I have used images of ships, equipment, uniforms, etc. Players who have access to images and information have before them a more realized world and can better visualize it.If your game is world spanning, or involves travel to other worlds or parallel universe or the like, then the players will want details, details, details. There is no need to write a novella, but anticipate questions, have answers prepared. Paint your world on a huge canvas using words as well as pictures. At the same time, do not drive yourself crazy trying to anticipate every single question that might be asked. If someone asks you for details about Madagascar, for example, and it has absolutely nothing to do with the plot at hand or the PC's background, then find out why the player wants to know. You have a life, players cannot expect you to be devoted so much of it to irrelevant details.
In my next post I will discuss the relationship between the GM and players and co-moderated games. Since it will be called There Can Be Only One, you may have a clue how I feel about the matter. :)