This article offers a detailed explanation on the Copyright Principle. After reading you’ll know where to look for proper resources.
By default I will assume none of the resources are made by you unless it’s some simple stuff. As a result you should mention every non-trivial resource in the acknowledgement part of your world.
If it is made by you, you should explicitly state that.
Nowadays there’re many ways to make your own resources. You don’t need to draw the image yourself. For example, you can play a 3D game and do a screenshot. That’s yours. There’re many fantastic 3D games out there that you can use. One notable example is Skyrim. You can literally get anything from it, such as characters, items, monsters, scenery and action. But to be able to achieve best visual effects, you need to add a lot of mods to it. Here is a great site to get mods and check some sample pictures, especially the media part.
If it is not made by you, you should explain why you can use it.
There’re many proper and legal ways to use materials created by others. I will list some common ones.
- Public Domain
Public domain lets you use a resource without any restriction. This can happen if the author release the resource into public domain or copyright time has expired.
openclipart.org is a great site to look for icon, symbol and UIs. All resources there are released into public domain. publicdomainvectors.org is also a similar site. For photos and pictures, publicdomainpictures.net is one site to look for.
Although the time for copyright to expire varies from country to country, it won’t last for more than 100 years. That is to say, ALL resources before 1920 are in public domain. There’s one particular type of resource you should be aware of: classic paintings.
This is a painting named Cabinet of Curiosities by Georg Hinz. You should immediately sense that this is a valuable resource. In fact you can crop many resources from this painting. I don’t need to say there’re tens of thousands of great paintings out there.
If you know the name of the painting you’re looking for, usually you can find it on Wikimedia Commons.
Once there was a great site for classic art, theAthenaeum. But it was dead by now. Pity. However, you can still use this artist list as a reference.
- Creative Commons License
Although there’re many variations of CC license, the core part is that you can freely use a resource as long a you credit the author.
For CC images, again Wikimedia Commons is a great place.
For CC sound effects, you can check http://soundbible.com/royalty-free-sounds-1.html and https://www.freesound.org/.
For CC music, you can check freemusicarchive.org.
- Custom License
There’re some friendly licenses to let you use resources for free.
Many stock photo sites use this method. For example Pexels and Pixabay. They allow you to use images even without attribution. But as a courtesy you should give credit to the author. Pixabay even has music and video you can use for free.
Here are some sound source websites. http://pocket-se.info/ and http://amachamusic.chagasi.com/ and http://www.freesfx.co.uk/ and http://www.senses-circuit.com/
Many of the sites above are in Japanese. This shouldn’t be a surprise if you know a bit about Japanese game industry. You can use google translate if you don’t read Japanese.
And I’d also like to mention deviantart.com. That’s a great site for images. However, different authors have different licenses. So be sure to read carefully or contact the authors before using their works.
- Internet Meme
Resources in this type generally includes emoji, gifs, funny video clips and so on. Strictly speaking, meme can cause copyright infringement. However, since everybody is using them everywhere and it can be hard to track the original author, I’ll give it a pass if you use them in your world.
- Promotional Material
Resources in this type generally includes posters, covers, themes, brochures and so on. These materials are meant to be spread as widely as possible. As a result, if you use these and give a full credit to the target, you’re actually helping them for free. It’s very less likely that the copyright holder will sue you. According to this logic I’ll give it a pass.
- Fair Use Doctrine
Fair use is a legal doctrine that promotes freedom of expression by permitting the unlicensed use of copyright-protected works in certain circumstances. The idea behind fair use is that copyright is established to encourage more people to do creations, and shouldn’t be a factor to stifle creativity. You can learn more about this concept on the Internet.
If you decide to apply fair use in your world resources, you need to justify your cause.